INTERNET-DRAFT J. Gao
Intended Status: Experimental
Expires: October 18, 2019 April 16, 2019
Flexible Session Protocol
draft-gao-flexible-session-protocol-02
Abstract
FSP is a connection-oriented transport layer protocol that provides
mobility and multihoming support by introducing the concept of 'upper
layer thread ID', which is associated with some shared secret that is
applied to protect authenticity of the origin of the FSP packets.
It introduces the concept of transmit transaction to facilitate a
quad-party sub-protocol for shared secret installation.
It provides transport layer features of zero round-trip connection
multiplication and on-the-wire compression, in addition to ubiquitous
message authentication with optional encryption service.
Status of this Memo
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Copyright and License Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
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document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1. High Mobility . . . . . . . . . . . . . . . . . . . . . . . 5
1.2. Requirements Language . . . . . . . . . . . . . . . . . . . 6
1.3. Conventions . . . . . . . . . . . . . . . . . . . . . . . . 6
2. Abbreviations and Idioms . . . . . . . . . . . . . . . . . . . 7
3. Key Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . 9
3.1. Underlying Layer Services Required . . . . . . . . . . . . 9
3.1.1. Packet Delivery . . . . . . . . . . . . . . . . . . . . 9
3.1.2. Network Address Change Notification . . . . . . . . . . 9
3.1.3. Network Congestion Control . . . . . . . . . . . . . . 10
3.2. Identifying Connection by Local ULTID . . . . . . . . . . . 10
3.3. Defending Against Connection Redirection with ICC . . . . . 10
3.4. Transmit Transaction . . . . . . . . . . . . . . . . . . . 10
3.5. Quad-party Session Key Installation Sub-protocol . . . . . 11
3.6. Zero Round-Trip Connection Multiplication . . . . . . . . . 12
4. Packet Structure . . . . . . . . . . . . . . . . . . . . . . . 13
4.1. FSP over UDP/IPv4 . . . . . . . . . . . . . . . . . . . . . 13
4.2. FSP over IPv6 . . . . . . . . . . . . . . . . . . . . . . . 13
4.3. Generic FSP Header . . . . . . . . . . . . . . . . . . . . 15
4.4. FSP Header Signature . . . . . . . . . . . . . . . . . . . 15
4.4.1 Header Stack Pointer . . . . . . . . . . . . . . . . . . 15
4.4.2 Major . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.4.3 Operation Code . . . . . . . . . . . . . . . . . . . . . 16
4.5. Preliminary FSP Packets . . . . . . . . . . . . . . . . . . 18
4.5.1. Connect Initialization . . . . . . . . . . . . . . . . 18
4.5.2. Acknowledgment to Connect Initialization . . . . . . . 19
4.5.3. Connect Request . . . . . . . . . . . . . . . . . . . . 20
4.6. Normal Fixed Header . . . . . . . . . . . . . . . . . . . . 21
4.7. Sink Parameter . . . . . . . . . . . . . . . . . . . . . . 23
4.8. Selective Negative Acknowledgment . . . . . . . . . . . . . 25
4.9. RESET . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
5. The Finite State Machine . . . . . . . . . . . . . . . . . . . 27
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5.1. NON_EXISTENT . . . . . . . . . . . . . . . . . . . . . . . 27
5.2. LISTENING . . . . . . . . . . . . . . . . . . . . . . . . . 27
5.3. CONNECT_BOOTSTRAP . . . . . . . . . . . . . . . . . . . . . 27
5.4. CONNECT_AFFIRMING . . . . . . . . . . . . . . . . . . . . . 28
5.5. CHALLENGING . . . . . . . . . . . . . . . . . . . . . . . . 28
5.6. ACTIVE{A.K.A. ESTABLISHED} . . . . . . . . . . . . . . . . 29
5.7. COMMITTING . . . . . . . . . . . . . . . . . . . . . . . . 29
5.8. COMMITTED . . . . . . . . . . . . . . . . . . . . . . . . . 30
5.9. PEER_COMMIT . . . . . . . . . . . . . . . . . . . . . . . . 30
5.10 COMMITTING2 . . . . . . . . . . . . . . . . . . . . . . . . 31
5.11 CLOSABLE . . . . . . . . . . . . . . . . . . . . . . . . . 31
5.12 PRE_CLOSED . . . . . . . . . . . . . . . . . . . . . . . . 32
5.13 CLOSED . . . . . . . . . . . . . . . . . . . . . . . . . . 32
5.14 CLONING . . . . . . . . . . . . . . . . . . . . . . . . . . 32
5.15 Passive Multiplication . . . . . . . . . . . . . . . . . . 33
6. End-to-End Negotiation . . . . . . . . . . . . . . . . . . . . 34
6.1. Connect Initialization . . . . . . . . . . . . . . . . . . 34
6.2. Response to Connect Initialization . . . . . . . . . . . . 35
6.3. Connection Incarnation Request . . . . . . . . . . . . . . 35
6.4. Connection Incarnation Response . . . . . . . . . . . . . . 36
6.5. The Last Confirmation . . . . . . . . . . . . . . . . . . . 37
6.6. Retransmission . . . . . . . . . . . . . . . . . . . . . . 37
7. Quad-party Session Key Installation . . . . . . . . . . . . . 37
7.1. API for Session Key Installation . . . . . . . . . . . . . 38
7.2. Time to Call API for Session Key Installation . . . . . . . 38
7.3. Time to Take New Session Key into Effect . . . . . . . . . 38
7.4. Generating the Initial Session Key . . . . . . . . . . . . 39
7.5. Internal Rekeying . . . . . . . . . . . . . . . . . . . . . 40
8. Send and Receive . . . . . . . . . . . . . . . . . . . . . . . 41
8.1. Packet Integrity Protection . . . . . . . . . . . . . . . . 41
8.1.1. Application of CRC64 . . . . . . . . . . . . . . . . . 41
8.1.2. Packet Authentication Only . . . . . . . . . . . . . . 41
8.1.3. Authenticated Encryption with Additional Data . . . . . 42
8.1.4 ICC of the Out-of-Band Packet . . . . . . . . . . . . . 43
8.2. Start a New Transmit Transaction . . . . . . . . . . . . . 43
8.3. Send a Pure Data Packet . . . . . . . . . . . . . . . . . . 44
8.4. Commit a Transmit Transaction . . . . . . . . . . . . . . . 44
8.4.1. Initiate Transmit Transaction Commitment . . . . . . . 44
8.4.2. Respond to Transmit Transaction Commitment . . . . . . 44
8.4.3. Finalize Transmit Transaction Commitment . . . . . . . 44
8.4.4. Time-out for Committing Transmit Transaction . . . . . 45
8.5. Retransmission . . . . . . . . . . . . . . . . . . . . . . 45
8.5.1. Calculation of RTT . . . . . . . . . . . . . . . . . . 45
8.5.2. Generation and transmission of SNACK . . . . . . . . . 45
8.5.3. Negative acknowledgment of Packets Sent . . . . . . . . 46
8.5.4. Retransmission Interval . . . . . . . . . . . . . . . . 46
8.6. Flow Control . . . . . . . . . . . . . . . . . . . . . . . 46
8.7. Congestion Control . . . . . . . . . . . . . . . . . . . . 47
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8.8. On-the-Wire Compression . . . . . . . . . . . . . . . . . . 48
8.9. Milk Like Payload and Minimal Delay Service . . . . . . . . 48
9. Graceful Shutdown . . . . . . . . . . . . . . . . . . . . . . 49
9.1. Initiation of Graceful Shutdown . . . . . . . . . . . . . . 49
9.2. Acknowledgment of Graceful Shutdown . . . . . . . . . . . . 50
9.3. Finalization of Graceful Shutdown . . . . . . . . . . . . . 50
9.4. Retransmission of RELEASE Packet . . . . . . . . . . . . . 50
10 Mobility and Multi-home Support . . . . . . . . . . . . . . . 50
10.1. Heartbeat Signals . . . . . . . . . . . . . . . . . . . . 50
10.2. Active Address Change Signaling . . . . . . . . . . . . . 51
10.3. Heuristic Remote Address Change Adaptation . . . . . . . . 51
10.4. Heuristic Address Change Acknowledgement . . . . . . . . . 52
10.5. NAT-traversal and Multihoming . . . . . . . . . . . . . . 52
10.6. Explicit Multi-home Informing . . . . . . . . . . . . . . 52
11 Connection Multiplication . . . . . . . . . . . . . . . . . . 53
11.1. Request to Multiply Connection . . . . . . . . . . . . . . 53
11.2. Response to Connection Multiplication Request . . . . . . 53
11.3. Duplicate Detection of Connection Multiplication Request . 54
11.4. Retransmission . . . . . . . . . . . . . . . . . . . . . . 55
11.5. Key Derivation for Branch Connection . . . . . . . . . . . 55
12 Timeouts and Abrupt Close . . . . . . . . . . . . . . . . . . 55
12.1. Timeouts in End-to-End Negotiation . . . . . . . . . . . . 55
12.2. Timeouts in Multiply . . . . . . . . . . . . . . . . . . . 56
12.3. Timeout of Transmit Transaction Commitment . . . . . . . . 56
12.4. Timeout of Graceful Shutdown . . . . . . . . . . . . . . . 56
12.5. Idle Timeout . . . . . . . . . . . . . . . . . . . . . . . 56
12.6. Session Key Timeout . . . . . . . . . . . . . . . . . . . 56
12.7. Abrupt Close . . . . . . . . . . . . . . . . . . . . . . . 57
13 Issues for Further Study . . . . . . . . . . . . . . . . . . . 57
13.1. Resolution of ULTID in DNS . . . . . . . . . . . . . . . . 57
13.2. Proxy Pattern for Syndicated Name Resolution . . . . . . . 57
13.3. Asymmetric Transmission . . . . . . . . . . . . . . . . . 58
14 Security Considerations . . . . . . . . . . . . . . . . . . . 59
14.1. Deny of Service Attack . . . . . . . . . . . . . . . . . . 59
14.2. Replay Attack . . . . . . . . . . . . . . . . . . . . . . 59
14.3. Passive Attacks . . . . . . . . . . . . . . . . . . . . . 59
14.4. Masquerade Attack . . . . . . . . . . . . . . . . . . . . 59
14.5. Active Man-In-The-Middle Attack . . . . . . . . . . . . . 59
14.6. Privacy Concerns . . . . . . . . . . . . . . . . . . . . . 59
15 IANA Considerations . . . . . . . . . . . . . . . . . . . . . 59
16 References . . . . . . . . . . . . . . . . . . . . . . . . . . 60
16.1. Normative References . . . . . . . . . . . . . . . . . . . 60
16.2. Informative References . . . . . . . . . . . . . . . . . . 62
17 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 65
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 65
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1. Introduction
Flexible Session Protocol is a connection-oriented transport layer
provides mobility, multi-homing and multi-path support by introducing
the concept of 'upper layer thread ID' (ULTID), which was firstly
suggested in [Gao2002].
An integrity check code (ICC) field associated with the ULTID is
designed in the FSP header to protect authenticity and optionally
privacy of the FSP packet. An FSP packet is assumed to originate from
the same source if the ICC value associated with certain destination
ULTID passes validation, regardless of the source or destination
address in the underlying layer.
ICC is either calculated by [CRC64] which protects FSP against
unintended modification, or a cryptographic hash function, or
cryptographically calculated with some Authenticated Encryption with
Additional Data ([R01]) algorithm, each of which requires a shared
secret key.
In the former case a weak key meant to obfuscate the CRC64 checksum
is agreed by the FSP participants. In the latter two cases, the
shared secret key is assumed to be installed by the upper layer
application (ULA).
The ULTID is assigned roughly the same semantics with Security
Parameter Index (SPI) in MOBIKE [RFC4555]. Either the weak key or the
shared secret key is indexed by the source or destination ULTID in
the local context of the sender or the receiver, respectively.
FSP facilitates secret key installation by introducing the concept of
transmit transaction. Mechanism of transmit transaction also provides
the session-connection synchronization service to the upper layer.
FSP is a transport layer protocol as specified in [RFC1122], provides
services alike TCP [STD5] to ULA, with session layer features as
suggested in [OSI/RM], most noticeably session-connection
synchronization. It can be argued that FSP makes it much more
flexible for the application layer protocols to adopt new key
establishment protocol/algorithm while offloading routine
authentication and optionally encryption of the data to the
underlying layers where it may be much easier to exploit hardware-
acceleration.
1.1. High Mobility
Here high mobility refers to scenarios such as high-speed train or
airplane.
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FSP solves somewhat coarse-grain or low-speed mobility problem. Fine-
grain or high-speed mobility is left to the underlying physical
network, which is semantics specified in [RFC1122]. To make mobility
support work effectively it is assumed that one end-node MUST keep
its lower layer address reasonably stable while the other end-node
SHOULD NOT change its lower layer address too frequently.
1.2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
In this document, these words will appear with that interpretation
only when in ALL CAPS. Lower case uses of these words are not to be
interpreted as carrying significance described in RFC 2119.
1.3. Conventions
Conventions in describing the finite state machine (FSM) of FSP are:
ESTABLISHED The string of alphabetic characters designates the
name of the state
[API: Reset] Upper Layer Application Programming Interface Call
{Notify} Call back/notify the upper layer application
{new context} Additional action before or after state transition
[Send OPCODE_OF_FSP_PACKET]
Send some FSP packet
[Retransmit OPCODE_OF_FSP_PACKET]
Retransmit some FSP packet
{On transient state Timeout}
Timed-out event
{&& additional condition}
Together with some additional condition
--> state transition
|-- branch
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2. Abbreviations and Idioms
o Connection
An FSP connection is the binding of two network nodes established
through some end-to-end negotiation process. It is identified by
the ULTID in the local context of each network node, respectively.
o EoT
A transmit transaction is said to reach End of Transaction (EoT) if
the EoT flag is set in a legitimate PURE_DATA, PERSIST, NULCOMMIT
or MULTIPLY packet. We said that the packet terminates the transmit
transaction if the EoT flag is set.
An FSP end node SHALL NOT send further data if it has initiated EoT
of its transmit direction unless a particular ACK_FLUSH packet is
received. The particular AKC_FLUSH packet MUST acknowledge not only
the packet with the EoT flag set but all of the packets sent before
the packet as well.
EoT, i.e. termination of transmit transaction is unilateral.
o FREWS
It stands for the Flag and advertised REceive Window Size. It is
the 32-bit combined word next to the ICC field in the normal FSP
fixed header.
o ICC
The Identity Check Code is a 64-bit value that depends on both the
session key and all of the headers of the FSP packet to include the
ICC, calculated with the same algorithm in the context of each FSP
participant.
Only a packet with correct ICC can be accepted by any FSP
participant as soon as the connection has been established.
Initially CRC64 is exploited to make a checksum that weekly
protects the FSP packet against unintentional modification. The
checksum is obfuscated with the initial session key to get the ICC.
After the ULA installed the long-term session key either some
cryptographic hash function or some Authenticated Encryption with
Additional Data algorithm shall be applied to obtain or check the
ICC.
o Session
An FSP session is the transport-layer association of two network
nodes. A full FSP session consists of one connection that was
established from scratch and all of its branches.
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However for this version of FSP specification the idioms session
and connection are interchangeable if not explicitly specified.
o Session Key
The session key is a bit string of at least 128 bits that means to
resist against masquerade attack. It is either initiated during the
end-to-end negotiation phase or installed by the ULA after the FSP
connection is established.
The session key installed by the ULA is called the long-term
session key. Here long-term means that the key could be used until
the packet sequence space is exhausted. The packet sequence space
is exhausted if the number of packets that use the same key reaches
or exceeds 2,147,483,647(2^31-1).
o SN
Sequence Number is the unsigned 32-bit integer number assigned to
every FSP packet except the preliminary packets.
Difference of two sequence number is represented by a 32-bit signed
integer. If the result of SN B subtracting SN A is greater than
zero, we say that B is greater than A and the packet of the
sequence number B is later than the packet of the sequence number
A, although the unsigned integer representation of B may be far
less that A. Consequently, as the result of A subtracting B is less
than zero, we say that A is less than B and the packet of the
sequence number A is earlier than the packet of the sequence number
A.
o Transmit Transaction
A transmit transaction of FSP is a sequence of FSP packets that
were sent and marked by the ULA as one continuous stream where all
packets in the stream must be acknowledged before any further
packet is allowed to be sent.
A PERSIST or MULTIPLY packet always starts a transmit transaction.
ACK_START, alias of NULCOMMIT, both start and terminate a payload-
less transmit transaction when it is exploited to acknowledge the
ACK_CONNECT_REQ or MULTIPLY packet.
o ULA
The Upper Layer Application.
o ULTID
The Upper Layer Thread Identifier (ULTID) is a 32-bit word that was
allocated by particular network end node of an FSP connection and
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is unique in the local context of the network end node.
Theoretically all of the ULAs of a network end node MAY establish
up to 2^31-1 FSP connections totally. Each connection MUST have a
unique thread identifier (ULTID) assigned in the local context of
the network end node.
A session or connection of FSP does not require a global ID.
3. Key Mechanisms
3.1. Underlying Layer Services Required
3.1.1. Packet Delivery
FSP requires that the underlying layer provides packet delivery
service.
In this version of FSP, when FSP is implemented in the IPv4 network,
every FSP packet MUST be encapsulated in a UDP [STD6] datagram
[RFC8085].
When FSP is implemented over IPv6, the FSP SHALL be the immediate
upper layer of IPv6 [RFC8200].
3.1.2. Network Address Change Notification
Network address change notification is mandatory only in the IPv6
network.
We split the IPv6 address of the IPv6 packet underlying FSP into
three parts. The leftmost 64-bit long word is the network prefix,
which SHOULD be the unique IPv6 prefix assigned to the host
[RFC8273]. The centermost 32-bit word is called the aggregation host
ID, and the rightmost 32-bit word is the ULTID. While the ULTID MUST
be kept stable even during the life of an FSP session, the network
prefix part MAY change when an endpoint is roaming. The aggregation
host ID may change as well. The network prefix part together with the
aggregation host ID part act as the traditional routing locator at
the network layer.
It is supposed that the network layer immediately notify FSP of the
network prefix and/or aggregation host ID change.
An participant of an FSP connection SHALL immediately notify its peer
whenever its underlying IPv6 address is changed with a KEEP_ALIVE
packet. The peer shall send packet to the participant that has
notified the address change with the new address.
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It is supposed that the packet to inform the remote end to update the
lower layer address association could reach its destination in a
satisfying success rate.
3.1.3. Network Congestion Control
It is supposed that end-to-end congestion control is provided at some
sub-layer of the network layer. Implementation of FSP MUST include a
congestion manager [RFC3124] if such sub-layer service of the network
layer is not provided.
3.2. Identifying Connection by Local ULTID
Each FSP connection prepares a pair of ULTIDs. ULTID is assigned
roughly the same semantics with the Security Parameter Index (SPI) in
IKE [RFC4301]. An ULTID uniquely indexes a connection in the local
context of an FSP end node. An FSP end node relies neither source IP
address nor destination IP address, except the ULTID part of the near
end's IPv6 address to identify an FSP connection.
Each ULTID is allocated in the local context of the two FSP
participant respectively. The source ULTID and the destination ULTID
of an FSP packet usually differ in their values. However, the secret
keys indexed in the local contexts of the two end-points must have
the same value.
3.3. Defending Against Connection Redirection with ICC
An integrity check code (ICC) field associated with the ULTID is
designed in the FSP header to protect authenticity and optionally
privacy of the FSP packet. An FSP packet is assumed to originate from
the same source if the ICC value associated with certain destination
ULTID passes validation, regardless of the source or destination
address in the underlying layer.
On initiating FSP takes use of [CRC64] to make checksum of the FSP
packet to protect it against unintentional modification. The checksum
is taken as the ICC.
After the ULA has installed a shared secret key, value of ICC is
calculated by firstly getting the secret key associated indexed by
the local ULTID, then calculating the tag value with the AES-GCM
[GCM] authenticated encryption with additional data algorithm [R01],
or calculating the message authentication code with the BLAKE2
algorithm [RFC7693].
3.4. Transmit Transaction
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FSP facilitates shared secret key installation by introducing the
concept of transmit transaction.
A transmit transaction of FSP is a sequence of FSP packets that were
sent and marked by ULA as one continuous stream where all packets in
the stream MUST be acknowledged before any further packet is allowed
to be sent.
A flag called 'End of Transaction' (EoT) is designed in the FSP
header. When it is set, it marks that the transmit transaction in the
direction from the source of the FSP packet towards the destination
of the FSP packet is committed.
3.5. Quad-party Session Key Installation Sub-protocol
It is proposed that it is the ULA to do key establishment and/or end-
point user-agent authentication while the FSP layer provides
authenticated, optionally encrypted data transfer service. It is
arguably much more flexible for the application layer protocols to
adopt new key establishment algorithm while offloading routine
authentication and optionally encryption of the data to the
underlying layers where it may be much easier to exploit hardware-
acceleration.
A dedicate application program interface (API) is designed for the
ULA to install the secret key established by the ULA participants.
Protocol for installation of the shared secret key is quad-party in
the sense that both the upper layer application and the FSP layer of
the two participant nodes MUST agree on the moment of certain state
to install the shared secret key.
The ULA installs the new secret key to the FSP layer. The FSP layer
SHALL make it sure that the new secret key is taken into effect
starting from the very first packet of the transmit transaction that
is immediately next to the transmit transaction where API for
installation of the new secret key is called.
By committing a transmit transaction a ULA participant clearly tells
the underlying FSP layer that the next packet sent MAY adopt a new
secret key. On receiving a packet with the EoT flag set the ULA is
informed that the next packet received MAY adopt a new shared secret
key.
The ULA participant that installs the new secret key firstly MUST be
the one that is committing a transmit transaction after it has
accepted peer's transmit transaction commitment.
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After the ULA install a new secret key every packet sent later than
the one with the EoT flag set MUST adopt the new secret key. The peer
MUST have commit a transmit transaction and it SHALL install the same
secret key on receiving the FSP packet with the EoT flag set.
The ULA SHOULD have installed the new shared secret key, or install
it instantly after accepting the packet with the EoT flag set.
If the new secret key has ever been installed the packet received
after the one with the EoT flag set MUST adopt the new secret key.
In a typical scenario the ULA endpoints first setup the FSP
connection where resistance against connection redirection is weakly
enforced by CRC64. After the pair of ULA endpoints establish a shared
secret key, they install the secret key and commit current transmit
transactions. Authenticity of the FSP packets sent later is
cryptographically protected by the new secret key and resistance
against various attacks is secured.
Although transmit transaction is actually uni-directional the secret
key is shared bi-directionally in this version of FSP.
3.6. Zero Round-Trip Connection Multiplication
An FSP connection MAY be multiplied to get a branch or branches of
the connection. In this version of FSP a branch connection SHALL NOT
be multiplied further, and only the connection where authenticity of
the packets is cryptographically protected may be multiplied.
The packet that carries the command to multiply an established FSP
connection MUST be sent from a new allocated local ULTID towards the
destination ULTID of the original connection. It is an out-of-band
packet in the context of the original connection and it MUST be
cryptographically protected by the secret key of the original
connection. The packet MAY carry payload.
The receiver of the packet MUST allocate a new local ULTID, accept
the optional payload in the new context associated with the new
ULTID, derive a new secret key from the secret key of the original
connection, and responds from the new context. The response MAY carry
payload.
The very first response packet MUST be protected by the new secret
key. The sender of the multiply command packet MUST automatically
inaugurate the same secret key, derived from the secret key of the
same original connection. And it MUST treat the response packet as
though a transmit transaction had been committed by the responder,
i.e. authenticity of the response packet is verified with the new
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secret key.
Thus the branch connection of a new pair of ULTIDs is established
with zero round-trip overhead. This mechanism may be exploited to
provide expedited data transfer or parallel data transfer service.
4. Packet Structure
4.1. FSP over UDP/IPv4
In this version of FSP, when FSP is implemented in the IPv4 network,
every FSP packet MUST be encapsulated in a UDP datagram. The UDP
datagram encapsulated the FSP packet SHALL have the checksum
disabled. The Source and the destination ULTIDs are put at the
leading position of the UDP payload. FSP fixed header, optional
extension headers and FSP payload follow the ULTIDs:
0 15 16 31
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Port | Destination Port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Upper Layer Thread ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Upper Layer Thread ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ FSP Fix Header ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Optional FSP Extension Headers ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ Optional FSP payload ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1 FSP over UDP
4.2. FSP over IPv6
When FSP is implemented over IPv6, the ULTID part is embedded in the
IPv6 address. FSP fixed header follows the IPv6 headers:
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~ IPv6 Header: ~
0 15 16 31
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| Traffic Class | Flow Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Payload Length | Next Header | Hop Limit |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Source Network Prefix +
| |
+ Source Address ----------------------------+
| Source Aggregation Host ID |
+ ----------------------------+
| Source Upper Layer Thread ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Destination Network Prefix +
| |
+ Destination Address ---------------------------------+
| Destination Aggregation Host ID |
+ ---------------------------------+
| Destination Upper Layer Thread ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ Optional IPv6 Headers ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ FSP Fix Header ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Optional FSP Extension Headers ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ Optional FSP payload ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2 FSP over IPv6
o Network Prefix
The leftmost 64-bit of the IPv6 address which MAY and usually do
have different value at the difference interface of an IPv6 end-
node.
o Aggregation Host ID
The left 32-bit part of the rightmost 64-bit long word of the IPv6
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address. All of the aggregation host ID parts of an IPv6 end-node's
IPv6 addresses MUST have the same value for this version of FSP.
4.3. Generic FSP Header
FSP headers include the fixed header and the extension headers. A
general fixed header consists of 20-byte operation-code specific
fields and a 32-bit FSP Header Signature. An extension header
consists an operation-code specific content and a 32-bit FSP Header
Signature. The length of the extension header content may be
variable, provided that the tail of the full extension header align
on 64-bit boundary.
0 31
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ Operation Code Specific Fields ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Header Signature |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3 FSP Header
4.4. FSP Header Signature
0 15 16 31
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Header Stack Pointer | Major | Operation Code|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4 FSP Header Signature
4.4.1 Header Stack Pointer
For the fixed header the header stack pointer is a 16-bit unsigned
integer that specifies the offset of the first octet of the payload.
For an extension header the header stack pointer is a 16-bit unsigned
integer that specifies the offset of the first octet of the very
extension header.
The offset that the header stack pointer specifies starts from the
begin of the FSP fixed header. If its value is 24 the header contains
it is the last extension header or the fix header without any
extension.
4.4.2 Major
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It is an octet states current FSP major version. For this FSP version
it MUST be 0.
It is not mandatory for different major versions of FSP to be
compatible.
4.4.3 Operation Code
It is an octet that stores the code of the command which indicates
the function of the packet.
Synonym Code Meaning
INIT_CONNECT 1 Initialize Connection
ACK_INIT_CONNECT 2 Acknowledge Initialization of Connection
CONNECT_REQUEST 3 Formally Request to Connect
ACK_CONNECT_REQ 4 Acknowledge the Connection Request
RESET 5 Reset a connection
Refuse to
establish the connection, or abort
connection.
NULCOMMIT 6 Commit without payload
The NULCOMMIT packet MUST be payload-
less, and its EoT flag MUST be set. It
MAY carry optional headers. It always
consumes a slot of the send sequence
space. It is to commit current transmit
transaction, otherwise the NULCOMMIT
packet itself SHALL just be skipped when
delivering data to ULA.
ACK_START 6 Alias of NULCOMMIT, ACKnowledgement to
start a connection
It is the acknowledgement to
ACK_CONNECT_REQ or MULTIPLY, to confirm
that the connection has been established
or multiplied. ACK_START, or NULCOMMIT,
MAY both start a payload-less transmit
transaction and terminate the transmit
transaction.
KEEP_ALIVE 7 Keep the peer alive
It is an out-of-band control packet
acting as the heart-beating signal. An
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out-of-band control packet does not
consume send sequence space itself. FSP
takes use of the KEEP_ALIVE packet to
inform the peer about the change of the
source IP addresses. Besides, when the
MIND flag is set, the KEEP_ALIVE packet
is meant to tell the peer which packets
should be retransmitted. If the End of
Transaction flag of the KEEP_ ALIVE
packet is set it is meant to forcefully
commit current transmit transaction of
the sender of the KEEP_ALIVE packet.
PERSIST 8 Make a connection persistent
It is meant to start a new transmit
transaction after a connection migrated
to CLOSABLE state. It can also
acknowledge ACK_CONNECT_REQ or MULTIPLY.
It MUST carry payload. It always
consumes a slot of the send sequence
space.
PURE_DATA 9 Pure Data
It does not carry any optional header.
ACK_FLUSH 10 ACKnowledge to remote end's commitment
(FLUSHing) of transmit transaction. It
is an out-of-band control packet like
KEEP_ALIVE. It is sent instantly on
having every packet of the last transmit
transaction received, meant to make
acknowledgment to the remote end and let
the remote end stop sending heart-beat
signals.
RELEASE 11 Release the connection
RELEASE packet does not carry payload
but it always consumes a slot of the
send sequence space. Only when each peer
has committed current transmit
transaction may a RELEASE packet sent
under the request of the ULA.
MULTIPLY 12 Multiply the connection
It is sent in the context of the
original connection and may carry
payload and/or optional headers as an
out-of-band packet.
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PEER_SUBNETS 17 Tell the remote end how to address
the sender of the packet in the reverse
direction. It is the code of the Sink
Parameter extension header.
SELECTIVE_NACK 18 Tell the remote end to retransmit
the packets that were negatively
acknowledged. It is the code of the
Selective Negative Acknowledgment
extension header.
4.5. Preliminary FSP Packets
Preliminary FSP packets are the packets exchanged during the end-to-
end negotiation phase of FSP connection establishment when it is
impossible to calculate ICC normally.
4.5.1. Connect Initialization
0 31
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Timestamp +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Init-Check-Code +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Salt |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Header Signature |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ Host Name of the Responder (optional) ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5 Connect Initialization
Operation Code of this type of packet is INIT_CONNECT.
o Timestamp
It is a 64-bit unsigned integer that represents number of
microseconds elapsed since 00:00, Jan.1, 1970, Coordinated
Universal Time. It may be exploited to synchronize the clocks of
the participants and/or estimate delay during data transmission in
the network.
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o Init-Check-Code
It is a 64-bit random [RFC4086] bit string that means to uniquely
associated with the connection initiated.
o Salt
It a 32-bit random bit string that may be exploited to make secret
key agreement.
o Host Name of the Responder
The optional payload of the Connect Initialization packet is the
host name, which is encoded in UTF-8 [RFC3629] and SHOULD be
resolvable in DNS, of the responder.
4.5.2. Acknowledgment to Connect Initialization
0 31
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Cookie +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Init-Check-Code +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ Sink Parameter ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Time Delta |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Header Signature |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6 Acknowledgment to Connect Initialization
Operation Code of this type of packet is ACK_INIT_CONNECT.
o Cookie
It is a 64-bit bit string cryptographically generated by the
responder in a represent-transfer state manner. More specifically
when the same timestamp, time delta, Init-Check-Code, salt, source
and destination ULTIDs are sent to the responder, the responder
MUST be able to generate the identical cookie value.
o Init-Check-Code
It MUST be identical to the corresponding field in the Connect
Initialization packet acknowledged.
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o Sink Parameter
It is an extension header specified in 4.7.
o Time Delta
It is a 32-bit signed integer which is the difference between the
near-end's time and the timestamp value sent in the Connection
Initialization packet. The units and the epoch of the near-end's
time value and the timestamp value MUST be the same. However, the
precision or resolution of the time delta value is chosen
arbitrarily by the responder.
4.5.3. Connect Request
0 31
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Time Stamp +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Init-Check-Code +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Salt |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Header Signature |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Initial Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Time Delta |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Cookie +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ Sink Parameter ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ Host Name of the Initiator (optional) ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7 Connect Request
Operation Code of this type of packet is CONNECT_REQUEST.
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The value of each field that has the identical name with the one in
the associated Connect Initialization and Acknowledgment to Connect
Initialization packet MUST be assigned the same value as in these two
packets, except header signature in the packet.
o Sink Parameter
It is an extension header specified in 4.7.
o Host Name of the Initiator
The optional payload of the Connect Request packet is the host
name, which is encoded in UTF-8 and SHOULD be resolvable in DNS, of
the initiator.
It could be exploited by the responder to look up the address of
the initiator that may receive packets in the reverse direction.
4.6. Normal Fixed Header
0 15 16 31
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Expected Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Integrity Check Code +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Advertised Receive Window Size |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Header Signature |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8 FSP Fixed Header
Operation Code of a normal fixed header may be ACK_CONNECT_REQ,
PURE_DATA, PERSIST, KEEP_ALIVE, ACK_FLUSH, RELEASE or MULTIPLY.
o Sequence Number
Each in-band FSP packet is assigned a 32-bit unsigned integer as
the sequence number. The sequence number assigned for in-band FSP
packets MUST be in strict order.
An out-of-band packet that has the operation code of KEEP_ALIVE,
ACK_FLUSH or MULTIPLY MUST be assigned a sequence number that falls
in the receive window.
o Expected Sequence Number
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It stores the earliest sequence number of the packets that were not
yet received in the receive window of the sender. It is an
accumulative acknowledgment. Any packet with the sequence number
before the received Expected Sequence Number is supposed to have
been received by the remote end.
o Integrity Check Code
The ICC.
o Flags
It is bit-field of width 8. From left to right:
- End of Transaction (EoT): If the EoT flag of a packet is set, it
is the last packet of a transmit transaction. A packet with the
EoT flag set MAY be the start and the single packet of the
transmit transaction as well.
- Minimal-Delay (MIND): If the MIND flag of the Connect Request or
Acknowledgment to Connect Request packet is set, the ULA prefers
minimal delay and is willing to tolerate packet loss. FSP SHALL
drop the packet received earliest when there is no enough receive
buffer so that the latest packet received can be saved and the
delay to deliver data to ULA is minimized.
If the MIND flag has been set the EoT flag of any following
packet is simply ignored.
The MIND flag of an FSP packet may be set only if the packet does
not belong to a compressed transmit transaction.
Payload of each FSP packet is delivered to the ULA as an
independent message if the MIND flag has been set.
- Compressed (CPR) If the CPR flag of the first packet of a
transmit transaction is set, compression is applied on the octet
stream of the payloads of the continuous packets that constitute
the transmit transaction, or to put it simply, the payload octet
stream of the transaction transaction. Such transmit transaction
is called a compressed transmit transaction.
When the CPR flag of a packet is set, CPR flag of each following
packet is ignored until reaching termination of the transmit
transaction.
If the payload octet stream of the transmit transaction is
compressed the Minimal-Delay flag of any packet in the transmit
transaction MUST be cleared.
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- ECN-Echo (ECE): The Explicit Congestion Notification Echo flag of
a packet is set if the sender of the packet has received an
underlying IPv6 packet with Congestion Experienced code point set
for its peer as stated in "The Addition of Explicit Congestion
Notification (ECN) to IP" [RFC3168].
- Send Rate Reduced (SRR): The SRR flag of each packet SHALL be set
as soon as the sender has received a legitimate packet with ECE
flag set and has informed the congestion manager to reduce the
send rate, until a sent packet with SRR flag set is acknowledged.
The remaining 3 bits are reserved.
o Advertised Receive Window Size
It is a 20-bit unsigned integer that stores number of the free
blocks in the receive buffer of the sender of the packet that
contains the receive window size field. It is count from the slot
meant to accept the packet with the expected sequence number.
The sender must ensure that the difference between the latest
sequence number sent out and the largest expected sequence number
received does not exceed the value of the latest advertised receive
window size received.
4.7. Sink Parameter
0 31
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ Addressable Network Prefixes ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Listener ID/Host ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Header Signature |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9 Sink Parameter
Operation Code in the Header Signature of this extension header is
PEER_SUBNETS.
o Addressable Network Prefixes
These are up to 4 64-bit words that specify the network prefixes of
the lower layer interfaces that are addressable by the receiver in
the reverse direction.
In this version of the FSP 'Addressable Network Prefixes' field is
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of fixed length. The last network prefix which is non-zero is the
last resort one. There MUST be at least one non-zero network
prefix. If there are more than one non-zero network prefixes those
other than the last resort are load-balanced preferred.
In an IPv6 network, the addressable network prefix is the leftmost
64 bits of the IPv6 address. The receiver of the Addressable
Network Prefixes SHALL send packet in the reverse direction, i.e.
to the sender of the field with the destination IPv6 address
generated by combining a preferred network prefix with the
aggregation host id and the ULTID part of the source address in the
IPv6 header of the received packet that eventually carries the
Addressable Network Prefixes.
Such feature MAY be exploited to handle links with unidirectional
connectivity, but it is NOT RECOMMENTED.
In an IPv4 network for compatibility with the IPv6 addressed ULA
the 64-bit word of the addressable network prefix specified is
composed as following Figure:
0 15 16 31
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x2002 (IPv6 6to4 prefix) |IPv4 address (leftmost 16 bits)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|IPv4 address(rightmost 16 bits)| UDP port number (16 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10 Addressable Network Prefix of FSP over UDP/IPv4
Sender of the Sink Parameter packet SHOULD be NAT-aware. If it is
able to obtain the from the NAT box (as defined in "Traditional IP
Network Address Translator (Traditional NAT)" [RFC3022]) through Port
Control Protocol (PCP) [RFC6887] SHOULD fill in the IPv4 address and
UDP port number fields with the public IP value that were obtained.
If it does not have such capability, it SHALL fill in the addressable
network prefix with all binary zeroes.
o Listener ID
It is the ULTID of the responder that is in LISTENING state.
o Host ID
It is the aggregation host id of the sender. It SHALL be 0 if it is
in the IPv4 network.
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4.8. Selective Negative Acknowledgment
0 31
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Gap Width |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
~ Further pairs of (Gap Width, Data Length) ~
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Acknowledgement Delay +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Out-band Serial Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Header Signature |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 11 Selective Negative Acknowledgment
The operation code of this type of extension header is SNACK. The
SNACK header contains the descriptor of the receive window gaps:
The descriptor itself is a list of entries. The length of the list
can be zero which means that there is no gap in the receive window.
If the list is not empty, each entry contains the width of one gap in
the receive window and the length of the continuously received data
following the gap, respectively. The unit of aforementioned length of
gaps or number of packets is buffer block.
o Acknowledgement Delay
A 64-bit unsigned integer specifies the delay in microseconds
between sending the packet containing the SNACK extension header
and accepting the last packet that is accumulatively acknowledged
by the SNACK extension header.
o Out-band Serial Number
The SNACK header contains a 32-bit out-band serial number as well.
Each time a packet that contains the SNACK header is sent the out-
band serial number shall increase by one. It is assumed that in the
life of the session no two packets have the same sequence number
and the same SNACK header serial number simultaneously.
4.9. RESET
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The 'RESET' packet is a special command packet meant to interrupt
connection setup process or disconnect abruptly. Operation Code of
the packet is RESET.
Structure of a RESET packet in C code snippet with unnamed union
applied:
struct FSP_RejectConnect
{
/* sequence numbers */
union
{
timestamp_t timeStamp;
struct
{
uint32_t initial;
uint32_t expected;
} sn;
};
/* uniqueness proof */
union
{
uint64_t integrityCode;
uint64_t cookie;
uint64_t initCheckCode;
};
/* bit field to describe reasons for reset */
uint32_t reasons;
$FSP_HeaderSignature hs;
};
When the RESET packet is the response to a Connect Initialization
packet both the timeStamp and the initCheckCode fields of the RESET
packet MUST be set to the same values of Time Stamp and Init-Check-
Code in the Connect Initialization packet, respectively.
When the RESET packet is the response to a Connect Request packet
both the timeStamp and the cookie fields of the RESET packet MUST be
set to the same value of Time Stamp and Cookie in the Connect Request
packet, respectively.
When the RESET packet is the response to a packet with a normal fixed
header, the sn.initial, the sn.expected and the integrityCode of the
RESET packet MUST be set as to specification of normal fixed header
field Sequence Number, Expected Sequence Number and Integrity Check
Code, respectively.
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5. The Finite State Machine
5.1. NON_EXISTENT
---[API: Listen]-->LISTENING
|--[API: Connect]-->CONNECT_BOOTSTRAP-->[Send INIT_CONNECT]
|--[API: Multiply]-->CLONING-->[Send MULTIPLY]
NON_EXISTENT is a pseudo-state before a connection is created by the
ULA calling API Listen, Connect or Multiply (or after a connection is
reset).
5.2. LISTENING
---[API: Reset]-->NON_EXISTENT
|<-->[Rcv.INIT_CONNECT]{&& accepted}[Send ACK_INIT_CONNECT]
|<-->[Rcv.INIT_CONNECT]{&& rejected}[Send RESET]
|<-->[Rcv.CONNECT_REQUEST]{&& duplication detected}
[Retransmit ACK_CONNECT_REQ]
|--[Rcv.CONNECT_REQUEST]-->{Notify}
|-->[API: Accept]
-->{new context}CHALLENGING-->[Send ACK_CONNECT_REQ]
|-->[API: Reject]-->[Send RESET] {abort new context, if any}
LISTENING is a state entered by the ULA calling API Listen.
5.3. CONNECT_BOOTSTRAP
---[API: Reset]-->NON_EXISTENT-->[Send RESET]
|--[Rcv.ACK_INIT_CONNECT]-->CONNECT_AFFIRMING
|-->[Send CONNECT_REQUEST]
|--[Rcv.RESET]-->NON_EXISTENT-->[Notify]
|--{On transient state Timeout}-->NON_EXISTENT-->[Notify]
CONNECT_BOOTSTRAP is a state entered by the ULA calling API Connect,
before receiving the acknowledgement of the remote end to the
connection initialization packet.
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5.4. CONNECT_AFFIRMING
---[API: Reset]-->NON_EXISTENT-->[Send RESET]
|--[Rcv.ACK_CONNECT_REQ]-->[Notify]
|-->{Callback return to accept}
|-->{EOT}
|-->{No Payload to Send}-->COMMITTING2-->[Send ACK_START]
|-->{Has Payload to Send}
|-->{ULA-flushing}-->COMMITTING2
-->[Send PERSIST with EoT]
|-->{Not ULA-flushing}-->PEER_COMMIT-->[Send PERSIST]
|-->{Not EOT}
|-->{No Payload to Send}-->COMMITTING-->[Send ACK_START]
|-->{Has Payload to Send}
|-->{ULA-flushing}-->COMMITTING
-->[Send PERSIST with EoT]
|-->{Not ULA-flushing}-->ESTABLISHED-->[Send PERSIST]
|-->{Callback return to reject]-->NON_EXISTENT-->[Send RESET]
|--[Rcv.RESET]-->NON_EXISTENT-->[Notify]
|--{On transient state Timeout}-->NON_EXISTENT-->[Notify]
CONNECT_AFFIRMING is a state entered by the ULA affirming to send
connect request after receiving the acknowledgement to the connection
initialization packet.
5.5. CHALLENGING
---[API: Reset]-->NON_EXISTENT-->[Send RESET]
|<-->[API: Send{new data}]{just pre-buffer}
|--[Rcv.ACK_START]
|-->{ULA-flushing}-->CLOSABLE-->[Notify]
-->[Send ACK_FLUSH]
|-->{Not ULA-flushing}-->PEER_COMMIT-->[Notify]
-->[Send ACK_FLUSH]
|--[Rcv.PERSIST]
|-->{EOT}
|-->{ULA-flushing}-->CLOSABLE-->[Notify]
-->[Send ACK_FLUSH]
|-->{Not ULA-flushing}-->PEER_COMMIT-->[Notify]
-->[Send ACK_FLUSH]
|-->{Not EoT}
|-->{ULA-flushing}-->COMMITTED-->[Notify]
-->[Send delay SNACK]
|-->{Not ULA-flushing}-->ESTABLISHED-->[Notify]
-->[Send delay SNACK]
|--[Rcv.RESET]-->NON_EXISTENT-->[Notify]
|--{On transient state Timeout}-->NON_EXISTENT-->[Notify]
CHALLENGING is a state entered by the ULA accepting the connection
request after a new connection context has been incarnated. The new
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connection is incarnated by the FSP context of the near end in the
LISTENING state as a legitimate CONNECT_REQUEST packet is received.
5.6. ACTIVE{A.K.A. ESTABLISHED}
---[API: Reset]-->NON_EXISTENT-->[Send RESET]
|--[API: Send{flush}]-->COMMITTING{Urge to commit}
|<-->[API: Send{more data}][Send PURE_DATA]
|--[Rcv.NULCOMMIT]
|-->PEER_COMMIT-->[Send ACK_FLUSH]-->[Notify]
|--[Rcv.PURE_DATA]
|--{Not EOT}-->[Send SNACK]-->[Notify]
|--{EOT}
|-->PEER_COMMIT-->[Send ACK_FLUSH]-->[Notify]
|--[Rcv.PERSIST]
|--{Not EOT}-->[Send SNACK early]
|--[EOT]
|-->PEER_COMMIT-->[Send ACK_FLUSH]-->[Notify]
|--[Rcv.MULTIPLY]{passive multiplication}
|--[Rcv.RESET]-->NON_EXISTENT-->[Notify]
|--{On Idle Timeout}-->NON_EXISTENT-->[Notify]
ACTIVE or ESTABLISHED is a state that the FSP participant has
finished end-to-end negotiation but has not committed current
transmit transaction nor fully received the latest transmit
transaction of the remote end.
5.7. COMMITTING
---[API: Reset]-->NON_EXISTENT-->[Send RESET]
|--[Rcv.ACK_FLUSH]-->COMMITTED-->[Notify]
|--[Rcv.NULCOMMIT]
|-->COMMITTING2-->[Send ACK_FLUSH]-->[Notify]
|--[Rcv.PURE_DATA]
|--{Not EOT}-->[Send SNACK]-->[Notify]
|--{EOT}-->COMMITTING2-->[Send ACK_FLUSH]-->[Notify]
|--[Rcv.MULTIPLY]{passive multiplication}
|--[Rcv.RESET]-->NON_EXISTENT-->[Notify]
|--{On Idle Timeout}-->NON_EXISTENT-->[Notify]
COMMITTING is a state that the FSP participant has committed the
transmit transaction but has not fully received the latest transmit
transaction of the remote end, nor the acknowledgement to the
transmit transaction commitment has been received.
The participant in COMMITTING state SHALL NOT transmit further data
until current transmit transaction commitment is acknowledged.
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5.8. COMMITTED
---[API: Reset]-->NON_EXISTENT-->[Send RESET]
|--[API: Send{more data}]-->ACTIVE-->[Send PERSIST]
|--[API: Send{flush}]-->COMMITTING-->{Flush the send queue}
|--[Rcv.NULCOMMIT]
|-->CLOSABLE-->[Send ACK_FLUSH]-->[Notify]
|--[Rcv.PURE_DATA]
|-->{Not EOT}-->[Send SNACK]-->[Notify]
|-->{EOT}
|-->CLOSABLE-->[Send ACK_FLUSH]-->[Notify]
|--[Rcv.PERSIST]
|-->{Not EOT}-->[Send SNACK]
|-->{EOT}-->CLOSABLE-->[Send ACK_FLUSH]-->[Notify]
|--[Rcv.MULTIPLY]{passive multiplication}
|--[Rcv.RESET]-->NON_EXISTENT-->[Notify]
|--{On Idle Timeout}-->NON_EXISTENT-->[Notify]
COMMITTED is a state that the FSP participant has committed current
transmit transaction and has received the acknowledgement to the
transmit transaction commitment, but has not fully received the
latest transmit transaction of the remote end.
5.9. PEER_COMMIT
---[API: Reset]-->NON_EXISTENT-->[Send RESET]
|--[API: Send{flush}]-->{Mark EoT or append NULCOMMIT}
|-->COMMITTING2-->{Do Send}
|--[API: Shutdown]-->{Append RELEASE}
|-->COMMITTING2-->{Do Send}
|<-->[API: Send{more data}][Send PURE_DATA]
|<-->[Rcv.PURE_DATA]{just prebuffer}
|<-->[Rcv.NULCOMMIT]-->[Send ACK_FLUSH]
|--[Rcv.PERSIST]
|-->{Not EOT}-->ACTIVE-->[Send SNACK]
|<-->{EOT}-->[Send ACK_FLUSH]
|--{&& is new transaction}-->[Notify]
|--[Rcv.MULTIPLY]{passive multiplication}
|--[Rcv.RESET]-->NON_EXISTENT-->[Notify]
|--{On Idle Timeout}-->NON_EXISTENT-->[Notify]
PEER_COMMIT is a state that the FSP participant has not committed
current transmit transaction but has fully received the latest
transmit transaction of the remote end, and the acknowledgement to
the transmit transaction commitment has not been received yet.
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5.10 COMMITTING2
---[API: Reset]-->NON_EXISTENT-->[Send RESET]
|--[API: Shutdown]-->{Append RELEASE}-->PRE_CLOSED-->{Do Send}
|<-->[Rcv.PURE_DATA]{just prebuffer}
|<-->[Rcv.NULCOMMIT]-->[Send ACK_FLUSH]
|--[Rcv.ACK_FLUSH]-->CLOSABLE-->[Notify]
|--[Rcv.PERSIST]
|-->{Not EOT}-->COMMITTING-->[Send SNACK]
|-->{EOT}-->[Send ACK_FLUSH]
|--{&& is a new transaction}-->[Notify]
|--[Rcv.MULTIPLY]{passive multiplication}
|--[Rcv.RELEASE]-->[Send ACK_FLUSH]-->[Notify]-->CLOSED
|--[Rcv.RESET]-->NON_EXISTENT-->[Notify]
|--{On Idle Timeout}-->NON_EXISTENT-->[Notify]
COMMITTING2 is a state that the FSP participant has committed current
transmit transaction and has fully received the latest transmit
transaction of the remote end, but the acknowledgement to the
transmit transaction commitment has not been received yet.
The participant in COMMITTING2 state SHALL NOT transmit further data
until current transmit transaction commitment is acknowledged.
5.11 CLOSABLE
---[API: Reset]-->NON_EXISTENT-->[Send RESET]
|--[API: Send{more data}]-->PEER_COMMIT-->[Send PERSIST]
|--[API: Send{flush}]-->COMMITTING2-->{Flush the send queue}
|--[API: Shutdown]-->{Append RELEASE}-->PRE_CLOSED-->{Do Send}
|<-->[Rcv.PURE_DATA]{just prebuffer}
|<-->[Rcv.NULCOMMIT]-->[Send ACK_FLUSH]
|--[Rcv.PERSIST]
|-->{Not EOT}-->COMMITTED-->[Send SNACK]
|-->{EOT}-->[Send ACK_FLUSH]
|--{&& is a new transaction}-->[Notify]
|--[Rcv.MULTIPLY]{passive multiplication}
|--[Rcv.RELEASE]-->[Send ACK_FLUSH]-->[Notify]-->CLOSED
|--[Rcv.RESET]-->NON_EXISTENT-->[Notify]
CLOSABLE is a state that the FSP participant has committed current
transmit transaction and has received the acknowledgement to the
transmit transaction commitment, and has fully received the latest
transmit transaction of the remote end.
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5.12 PRE_CLOSED
---[API: Reset]-->NON_EXISTENT-->[Send RESET]
|--[Rcv.ACK_FLUSH]-->CLOSED-->[Notify]
|--[Rcv.RELEASE]-->[Notify]-->CLOSED
|--[Rcv.RESET]-->NON_EXISTENT-->[Notify]
|--{On transient state Timeout}-->CLOSED-->[Notify]
PRE_CLOSED is a state entered by the ULA calling the API Shutdown in
CLOSABLE state.
5.13 CLOSED
|--{On Recycling Needed}-->NON_EXISTENT
CLOSED is a state migrated from PRE_CLOSED state on receiving a
legitimate RELEASE packet from the remote end.
Unlike TCP [STD7], CLOSED state in FSP is not fictional. Instead a
connection context MAY persist in CLOSED state until the session key
runs out of life, or the host system needs to recycle the resource
allocated to the CLOSED session. A connection in CLOSED state MAY be
resurrected.
5.14 CLONING
---[API: Reset]-->NON_EXISTENT
|<-->[API: Send{new data}]{just prebuffer}
|<-->[Rcv.PURE_DATA]{just prebuffer}
|--[Rcv.ACK_START]
|--{&& Not ULA-flushing}-->PEER_COMMIT
|-->[Send ACK_FLUSH]-->[Notify]
|--{&& ULA-flushing}-->CLOSABLE
|-->[Send ACK_FLUSH]-->[Notify]
|--[Rcv.PERSIST]
|-->{Not EOT}
|--{&& Not ULA-flushing}-->ACTIVE
|-->[Send SNACK]-->[Notify]
|--{&& ULA-flushing}-->COMMITTED
|-->[Send SNACK]-->[Notify]
|-->{EOT}
|--{&& Not ULA-flushing}-->PEER_COMMIT
|-->[Send ACK_FLUSH]-->[Notify]
|--{&& ULA-flushing}-->CLOSABLE
|-->[Send ACK_FLUSH]-->[Notify]
|--[Rcv.RESET]-->NON_EXISTENT-->[Notify]
|--{On transient state Timeout}-->NON_EXISTENT-->[Notify]
CLONING is a state entered by ULA calling the API Multiply from any
state that may accepting an out-of-band packet.
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5.15 Passive Multiplication
{ACTIVE, COMMITTING, COMMITTED, PEER_COMMIT, COMMITTING2, CLOSABLE}
|-->/MULTIPLY/-->[API{Callback}]-->{new context}CONNECT_AFFIRMING
|-->[{Return Accept}]
|-->{has payload prebuffered}-->{do respond}
|-->{without payload}-->[Prebuffer ACK_START]-->{do respond}
|-->[{Return Reject}]-->{abort creating new context}[Send RESET]
In the ACTIVE, COMMITTING, COMMITTED, PEER_COMMIT, COMMITTING2 or
CLOSABLE state an FSP end node MAY accept its peer's connection
multiplication request and transit to the unnamed, temporary passive
multiplication state.
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6. End-to-End Negotiation
End-to-end negotiation of FSP session occurs in the connection
establishment phase. Connection establishment process of FSP consists
of two and a half pairs of packet exchanges for connection
initialization, connection incarnation and the last confirmation.
During the process various optional header or payload MAY be carried
in the FSP preliminary packets to negotiate end-to-end session
parameters.
6.1. Connect Initialization
The initiator sends the INIT_CONNECT packet to the responder:
(INIT_CONNECT, Timestamp, Init-Check-Code, Salt [, Responder's Host
Name])
Connection initialization MAY be syndicated with optional address
resolution at the gateway in the IPv6 network by carrying the
responder's host name in the INIT_CONNECT packet.
If it does carry the responder's host name it MUST take the link-
local interface address [RFC4291] as the source IPv6 address and the
default link-local gateway address, FE80::1, as the destination IPv6
address no matter whether the global unicast IP address of the
default gateway is configured.
If the gateway that relays the INIT_CONNECT packet finds that the
responder is on the same link-local network with the initiator it
SHALL change the source and the destination IP addresses of the
INIT_CONNECT packet to the link-local IP addresses of the initiator
and the responder respectively, and relay the packet onto the same
link-local network.
On receiving the INIT_CONNECT packet that carries the responder's
host name the link-local gateway MUST resolute the responder's global
unicast IPv6 address and map the initiator's global unicast IPv6
address, and replace the destination and source address of the
INIT_CONNECT packet respectively, unless it finds that the initiator
and the responder are on the same link-local network, where the
gateway SHALL process the packet as stated in the previous statement.
The gateway SHALL silently ignore the INIT_CONNECT packet if it is
unable to resolve the IP address of the responder.
If the destination address is the default link-local gateway address
while the INIT_CONNECT does not carry the responder's host name
payload, it is supposed that the gateway is the intent destination of
the connection to initialize.
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6.2. Response to Connect Initialization
The responder sends acknowledgment to the initiator:
Case 1: (ACK_INIT_CONNECT, Cookie, Init-Check-Code Reflected, Time-
delta, Responder's Sink Parameter)
Case 2: (RESET, Timestamp Reflected, Init-Check-Code Reflected,
Reason of Failure)
In case 1 the responder is ready to accept the connection. It SHALL
NOT make state transition on receiving INIT_CONNECT packet. It SHALL
generate a cookie which is meant to be reflected by the initiator.
The responder MUST send the ACK_INIT_CONNECT packet with the new
allocated local ULTID instead of the original listening ULTID. The
initiator should be able to find out the original listening ULTID by
searching its own connection context.
In the Responder's Sink Parameter the original listener ULTID MUST be
set to the right value.
In case 2 the responder refuses to accept the connection. It SHALL
send back a RESET packet with the listening ULTID as the source
ULTID.
In either case the destination address of the packet sent back MUST
be set to the source address of the corresponding Connect
Initialization packet whose source and destination address MAY be
updated by some intermediary such as the link-local gateway of the
initiator.
6.3. Connection Incarnation Request
(CONNECT_REQUEST, Timestamp, Init-Check-Code, Salt, Cookie Reflected,
Time-delta Reflected, Initial SN, Initiator's Sink Parameter [,
Initiator's Host Name])
The initiator accepts the Response to Connect Initialization packet
if and only if both the destination ULTID of the response packet
matches the source ULTID of the connect initialization packet and the
Init-Check-Code reflected in the response packet matches the Init-
Check-Code in the connect initialization packet.
If the response packet is accepted the initiator formally requests to
establish the connection by sending the CONECT_REQUEST packet.
In the CONNECT_REQUEST packet the value of the Timestamp, the Init-
Check-Code and the Salt field MUST be the same as in the INIT_CONNECT
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packet while the value of the Cookie Reflected field and the Time-
delta Reflected field MUST be the same as in the ACK_INIT_ CONNECT
packet, respectively.
The initiator MUST send the packet towards the remote ULTID that the
responder has preserved and sent with the ACK_INIT_CONNECT packet. It
MUST fill the original listener ID field in the Initiator's Sink
Parameter with the right value.
The source address of the CONNECT_REQUEST packet MUST be set to the
destination address of the received ACK_INIT_CONNECT packet, while
the network prefix and host-id part of the destination address MUST
be set to the source address of the received ACK_INIT_CONNECT packet
in the IPv6 network.
The initiator SHALL save the cookie value that the responder has
given to make up the weak session key.
The initiator MUST fill the Initial SN field with the sequence number
of the packet that will follow CONNECT_REQUEST. The CONNECT_REQUEST
packet is payload free and does not consume the sequence space.
The optional fields Initiator's Host Name is put as the payload of
the CONNECT_REQUEST packet. If presented it MAY be exploited by the
responder as the last resort to resolute the most recent IP address
of the initiator in some extraordinary scenarios such as the
initiator has hibernated for a considerably long time.
6.4. Connection Incarnation Response
Case 1: (ACK_CONNECT_REQ, Initial SN, Expected SN, ICC, FREWS[,
Payload])
Case 2: (RESET, Timestamp Reflected, Copy of Cookie Reflected, Reason
of Failure)
The responder responds as in case 1 if the reflected cookie was
validated, resources were successfully allocated and the initial
context of the connection was setup. Otherwise it SHOULD respond as
in case 2.
The Initial SN in case 1 is the initial sequence number of the
responder. The responder should fill in the field with a random 32-
bit unsigned integer. As the ACK_CONNECT_REQ packet may carry payload
the sequence number of the responder starts from the ACK_CONNECT_REQ
packet.
The Expected SN MUST equal to the Initial SN specified in the
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corresponding CONNECT_ REQUEST packet.
6.5. The Last Confirmation
Case 1: (ACK_START, Initial SN, Expected SN, ICC, FREWS)
Case 2: (PERSIST, Initial SN, Expected SN, ICC, FREWS, payload)
Case 3: (RESET, Initial SN, Expected SN, ICC, Reason of Failure)
The initiator of the connection MUST eventually confirm to the
responder that the connection is established by sending a payload-
less ACK_START packet (case 1) or a PERSIST packet with payload (case
2).
Of course the initiator MAY quit to establish the connection by
sending a legitimate RESET packet (case 3).
6.6. Retransmission
The initiator SHALL retransmit the INIT_CONNECT packet if the
corresponding ACK_INIT_CONNECT packet is not received in some limit
time (by default 15 seconds).
The initiator SHALL retransmit the CONNECT_CONNECT packet if the
corresponding ACK_CONNECT_REQ packet is not received in some limit
time (by default 15 seconds).
The responder SHALL NOT retransmit ACK_INIT_CONNECT or
ACK_CONNECT_REQ packet.
The initiator SHOULD retransmit the right INIT_CONNECT packet or
CONNECT_CONNECT packet until the legitimate ACK_CONNECT_REQ packet is
eventually received.
It SHALL give up if the time starting from the very first
INIT_CONNECT packet was sent has exceed a longer timed-out value (by
default 60 seconds) before the legitimate ACK_CONNECT_REQ packet is
received.
7. Quad-party Session Key Installation
It assumes that in the scenarios applying FSP it is the ULA to do key
establishment and/or end-point authentication while the FSP layer
provides authenticated, optionally encrypted data transfer service.
Together they establish a secure channel between two application end-
points.
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Protocol for installation of the shared secret key is quad-party in
the sense that both the upper layer application and the FSP layer of
both the participant nodes MUST agree on the moment of certain state
to install the shared secret key.
It is arguably much more flexible for the application layer protocols
to adopt new key establishment algorithm while offloading routine
authentication and optionally encryption of the data to the
underlying layers where it may be much easier to exploit hardware-
acceleration.
7.1. API for Session Key Installation
A dedicate application program interface (API) is designed for the
ULA to install the secret key established by the ULA participants.
The API SHOULD take four parameters:
- A 'handle' to state the connection context for installing the
session key
- A octet string of initial key materials (IKM)
- An integer to state the length of IKM. The unit is octet.
- An integer to state the desired length of the effective session key
if AEAD is applied. The unit is bit. For this version of FSP desired
length of the effective session key is either 128 or 256.
7.2. Time to Call API for Session Key Installation
The ULA participant that installs the new secret key firstly MUST be
the one that is committing a transmit transaction after it has
accepted peer's transmit transaction commitment.
In a typical scenario the ULA endpoints first setup the FSP
connection where resistance against connection redirection is weakly
enforced by CRC64.
After the pair of ULA endpoints establish a shared secret key, they
install the secret key and commit current transmit transactions.
Authenticity of the FSP packets sent later is cryptographically
protected by the new secret key and resistance against various
attacks is secured.
7.3. Time to Take New Session Key into Effect
The FSP layer SHALL make it sure that the new secret key is taken
into effect starting from the very first packet of the transmit
transaction that is next to the transmit transaction whose context is
where the new secret key is installed. Although transmit transaction
is actually uni-directional the secret key is shared bi-directionally
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in this version of FSP.
By committing a transmit transaction a ULA participant clearly tells
the underlying FSP layer that the next packet sent MAY adopt a new
secret key. On receiving a packet with the EoT flag set the ULA is
informed that the next packet received MAY adopt a new shared secret
key.
After the ULA install a new secret key every packet sent later than
the one with the EoT flag set MUST adopt the new secret key. The peer
MUST have commit a transmit transaction and it SHALL install the same
secret key on receiving the FSP packet with the EoT flag set.
The ULA SHOULD have installed the new shared secret key, or install
it instantly after accepting the packet with the EoT flag set. If the
new secret key has ever been installed the packet received after the
one with the EoT flag set MUST adopt the new secret key.
7.4. Generating the Initial Session Key
When the ULA install the secret key, it is required to provide the
initial key material which might have unbalanced bit randomness, not
the session key itself. HMAC-based Extract-and-Expand Key Derivation
Function (HKDF) [RFC5869] is applied to generate the initial session
key.
Given raw key material ikm, length of the ikm nB in octets, intended
master key length lenb in bits, || is octet string concatenation,
If HMAC only is designated, the nB octets of ikm is hashed into 64
octets which is taken as the master key.
If AEAD is designated, the initial session key, or the first secret
key for packet authentication and payload encryption is obtained as
specified in [RFC5869]:
Key Extract phase,
Let Km = BLAKE2(zeros || ikm) , where
zeros is 32 octets of integer 0
BLAKE2b algorithm without key is applied.
The result Km is the master key.
Key Expand phase,
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Let Ks = BLAKE2(Km, info) , where
Km is the master key generated in previous phase,
info is concatenation of the arbitrary ASCII string "Establishes
an FSP session", which is 26-octet long, 3 octets of integer 0,
and 1 octet of integer 1.
BLAKE2b algorithm with key is applied. The key applied MUST be the
master key Km.
The result Ks is the initial session key, or the first secret key
for packet authentication and payload encryption.
For this version FSP Ks is a fixed-length AES key together with a
4-octet salt. The salt is meant to be passed to AES-GCM as the
initialization vector together with the sequence number and
expected sequence number fields in the normal FSP fixed header:
0 31
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Salt |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Expected Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 12 Formation of Initialization Vector
7.5. Internal Rekeying
In this version of FSP it is forced to re-key on sending or receiving
every 536870912? (2^29) packets.
Let Ks' = BLAKE2(Km, H || info') , where:
Km is the master key generated as in section 7.4.
H is the 16-octet internal hash sub-key of AES-GCM of previous
session key,
info' is concatenation of the arbitrary ASCII string "Sustains an
FSP connection", which is 26-octet long
and the 4 octets in network order of the 32-bit unsigned integer
that specifies the batch index of the session key.
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BLAKE2b algorithm with key is applied. The key applied MUST be the
master key Km.
The result Ks' is the new session key, together with the new salt
meant to be form the IV.
The batch index of the initial session key is 1, and it is increased
by 1 every time before it is to re-key.
8. Send and Receive
8.1. Packet Integrity Protection
8.1.1. Application of CRC64
Starting from ACK_CONNECT_REQUEST, until the ULAs have installed the
shared secret CRC64 is applied to calculate the value of the ICC
field. The algorithm:
1.Take pair of the ULDs as the initial value of accumulative CRC64
The pair of the ULDs is composed of the near end's ULTID and the
remote end's ULTID, where the former is the leftmost 32 bits and
the latter is the rightmost 32 bits of initial value for the send
direction, and the order is reversed for the receive direction.
2.Accumulate the value of the Init-Check-Code field
3.Accumulate the value of the Cookie field successively
4.Accumulate the combined value of the salt and the timeDelta field
where the former is the leftmost 32 bits and the latter is the
rightmost 32 bits
5.Accumulate the value of the Time Stamp field
6.Save the accumulated CRC64 value
as the pre-computed CRC64 value.
When calculate the value ICC of a particular FSP packet, firstly set
ICC to the pre-computed CRC64 value, then calculate the CRC64
checksum of the whole FSP packet, while ULTIDs are NOT included if
the FSP packet is encapsulated in UDP. The result is set as the final
value of the ICC field.
8.1.2. Packet Authentication Only
The ULA designates the FSP layer to either applying HMAC only or
applying AEAD.
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If the HMAC flag of a packet is set the pre-designated cryptographic
hash function SHALL be applied to get the message authentication code
(MAC) of the whole packet. Each FSP version MUST designate one and
only one particular cryptographic hash function.
For this FSP version, BLAKE2 [RFC7693] is designated as the
cryptographic hash function. The input key is the secret key that has
been derived from the master key installed by the ULA. The input data
is the full FSP packet, where the ICC field is pre-filled the pair of
the ULDs. As in making CRC64 checksum, the pair of the ULDs is
composed of the near end's ULTID and the remote end's ULTID, where
the former is the leftmost 32 bits and the latter is the rightmost 32
bits of initial value for the send direction, and the order is
reversed for the receive direction.
The hash result is truncated to 64 bits to get the final ICC.
8.1.3. Authenticated Encryption with Additional Data
FSP provides per-packet authenticated encryption service. Only one
authenticated encryption algorithm is allowed for a determined
version of FSP. For this FSP version, the authenticated encryption
algorithm selected is GCM-AES [GCM][AES], it is applied to protect
integrity of the full FSP packets and privacy of the payload. The
length of the session key is determined by the ULA. The four inputs
to GCM-AES authenticated encryption are:
K: the key derived by the master key installed by ULA.
IV: the initial vector, 96-bit string made by concatenating a 32-bit
salt, the 32-bit sequence number of the packet and the 32-bit
expected sequence number field of the packet. The salt is derived by
the master key installed by ULA.
P: the plaintext are the bytes following the fixed header up to the
end of the original payload
AAD: additional authenticated data, from the source ULTID to the last
byte of the fixed header. The source ULTID is stored in the leftmost
32-bit of the ICC field while the destination ULTID is stored in the
rightmost 32-bit of the ICC field before the ICC value is calculated.
The length of the authentication tag MUST be 64 bits for FSP version
0 and 1. The authentication tag is stored in the ICC finally. The
inputs to GCM-AES decryption are:
K: the key installed by ULA.
IV: the initial vector, 96-bit string made by concating consisted of
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the 32-bit salt, the 32-bit sequence number of the packet and the 32-
bit expected sequence number field of the packet.
C: the ciphertext are the bytes following the fixed header up to the
end of the received payload
AAD: additional authenticated data, from the source ULTID to the last
byte of the fixed header. The source ULTID is stored in the leftmost
32-bit of the ICC field while the destination ULTID is stored in the
rightmost 32-bit of the ICC field before the ICC value is calculated
T: The authentication tag, which is fetched from the ICC field
received
Only when the outputs of GCM-AES decryption tell that the
authentication tag passed verification may the receiver deliver the
decrypted payload to the ULA.
8.1.4 ICC of the Out-of-Band Packet
When calculating the ICC of an out-band packet (KEEP_ALIVE, ACK_FLUSH
or MULTIPLY), the ExpectedSN field SHALL be filled with zero before
GCM-AES is applied to obtain the ICC value. After the ICC field is
set the ExpectiedSN field is set to the serial number of the out-of-
band packet, which is taken as the second salt as well.
When validating the received ICC the second salt value SHALL be
extracted from the ExpectedSN field of the received out-of-band
packet at first. Then the ExpectedSN field of the received MULTIPLY
packet SHALL be set to zero. Finally GCM-AES description is applied
and the ICC value is checked.
To get or check the ICC of the out-of-band packet the original salt
value that is set on deriving the session key and stored in the
internal security context MUST be XORed with the second salt value
before applying GCM-AES. Instantly after GCM-AES is applied the
original salt value MUST be recovered.
8.2. Start a New Transmit Transaction
The responder starts AND terminates a transmit transaction by send
the ACK_CONNECT_REQ packet.
The initiator starts a new transmit transaction by sending a PERSIST
packet:
(PERSIST, SN, ExpectedSN, ICC, FREWS, Payload)
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Or starts AND terminates a transmit transaction by send the ACK_START
packet:
(ACK_START, SN, ExpectedSN, ICC, FREWS [, Sink Parameter])
8.3. Send a Pure Data Packet
(PURE_DATA, SN, ExpectedSN, ICC, FREWS, Payload)
After a new transmit transaction has been started further PURE_DATA
packet MAY be sent until a packet with EoT flag set is sent.
8.4. Commit a Transmit Transaction
8.4.1. Initiate Transmit Transaction Commitment
A participant of an FSP connection MAY notify its peer that a
transmit transaction shall be committed by setting the EoT flag of
the last packet of the transmit transaction, be it PERSIST,
ACK_START, PURE_DATA or MULTIPLY.
8.4.2. Respond to Transmit Transaction Commitment
(ACK_FLUSH, SN, ExpectedSN, ICC, FREWS)
If and only if all of the packets in a transmit transaction has been
received MAY ACK_FLUSH packet be sent.
Whenever a legitimate packet falls in the receive window of the
receiver, and the packet fills in the last gap of the sequence of
current transmit transaction on receiving direction, or the packet
with same sequence number has been accepted already, a responding
ACK_FLUSH SHALL be sent back immediately, and the FSP layer MUST
immediately notify the ULA that a transmit transaction has been
committed.
The sequence number (SN) of the ACK_FLUSH packet MUST equal the
latest sequence number of the legitimate packets that have been sent.
The out-of-band serial number SHALL increase by one whenever a new
ACK_FLUSH packet is sent.
8.4.3. Finalize Transmit Transaction Commitment
After receiving the ACK_FLUSH packet the sender of the EoT flag
migrates to the COMMITTED or CLOSABLE state from the COMMITTING or
COMMITTING2 state, respectively.
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8.4.4. Time-out for Committing Transmit Transaction
The ULA SHALL be timed-out if there is no packet was acknowledged in
some hard-coded time-out. For this version of FSP the time-out is set
to 30 seconds.
8.5. Retransmission
8.5.1. Calculation of RTT
Initial round trip time (RTT) for the Connection Initiator: Equals to
the mean of the time elapsed when ACK_ INIT_CONNECT was received
since INIT_CONNECT was sent, and the time elapsed till
ACK_CONNECT_REQ was received since CONNECT_REQUEST was sent.
Initial RTT for the Connection Responder: Equals to the time elapsed
when the ACK_START or the first PERSIST packet was received since
ACK_CONNECT_REQ was sent.
Initial RTT for the Initiator of Connection Multiplication: Equals to
the time elapsed when the first PERSIST packet was received since
MULTIPLY was sent.
Initial RTT for the Responder of Connection Multiplication: Equals to
the most recent RTT of the multiplied connection.
Each time a SNACK or an accumulated acknowledgment is received the
round trip time of the packet with most expected SN is calculated.
The round trip time is the difference between the time when the
KEEP_ALIVE packet that carried the acknowledgement was received and
the time when the original packet was sent, minus the delay given in
the SNACK optional header of the KEEP_ALIVE packet. Suppose the
result is RTT_now, then:
RTT_new = (RTT_old + RTT_now) / 2
8.5.2. Generation and transmission of SNACK
Whenever the receiver receives a packet it SHALL shift the time to
send next heartbeat signal earlier to the time of RTT since current
time, if the time to send next heartbeat signal used to be later. If
the time is already earlier than the time of RTT since current time,
it needs not be shifted.
On the time to send the heartbeat signal the FSP node generates the
SNACK header, then generate and send a new KEEP_ALIVE or ACK_FLUSH
packet to carry the SNACK header. It SHALL send an ACK_FLUSH if it is
in PEER_COMMIT, COMMITTING2 or CLOSABLE state, otherwise it SHALL
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send a KEEP_ALIVE packet.
8.5.3. Negative acknowledgment of Packets Sent
Both the ACK_FLUSH and the KEEP_ALIVE packet in FSP carry the SNACK
extension header, although number of gap descriptors in the SNACK
extension header in the ACK_FLUSH packet MUST be 0. We call them
SNACK packets. A SNACK packet P1 is said to be later than P0, if and
only if SN of P1 is later than SN of P0, or SN of P1 equals SN of P0
while the out-of-band sequence number of P1 is later than the out-of-
band sequence number of P0. If the latest SNACK packet is ACK_FLUSH,
all the packets with the sequence number later that the expected
field of the packet are assumed to be negatively acknowledged.
By convention when we specify the range, the left square bracket
meant to be inclusive, while the right parenthesis meant to be
exclusive, the packets with SN in the ranges:
[expectedSN, expectedSN + 1st Gap Width),
[expectedSN + 1st Gap Width + 1st Data Length,
expectedSN + 1st Gap Width + 1st DataLength + 2nd Gap Width),
...
[expectedSN + 1st Gap Width + 1st Data Length
+ ... + (n-1)th Gap Width + (n-1)th Data Length,
expectedSN + 1st Gap Width + 1st DataLength
+ ... + n-th Gap Width),
together with the packets with SN later than {expectedSN + 1st Gap
Width + 1st DataLength + ... + n-th Gap Width} are assumed to be
negatively acknowledged, if the latest SNACK packet is KEEP_ALIVE.
8.5.4. Retransmission Interval
Any packet sent 4 times RTT earlier that is unacknowledged SHALL be
retransmitted as soon as possible.
FSP does not exploit Exponential backoff on setting retransmission
interval. However, retransmission is subjected to send rate control
at the underlying congestion management service sub-layer.
8.6. Flow Control
The participants of an FSP connection negotiate the initial receive
window size with the FREWS field in the ACK_CONNECT_REQUEST packet,
and the first PERSIST or ACK_START packet that acknowledges the
ACK_CONNECT_REQUEST packet, respectively. The receive window size
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SHALL NOT be less than 4 and SHALL be less than 2^24.
An FSP participant advertises current receive window size in the
FREWS field.
An FSP participant SHALL NOT send a packet whose sequence number is
later than the value of the ExpectedSN field plus the advertised
receive window size, where both value come from the very packet
received with the latest sequence number.
8.7. Congestion Control
FSP supposes that end-to-end congestion control is provided by some
shim layer, such as the congestion manager [RFC3124] between the
"traditional" IP layer and the FSP transport layer. The shim layer is
considered as a sub-layer of the network layer. Implementation of FSP
MUST provide such shim layer if the network layer of the end node
does not provide end-to-end congestion management service.
FSP layer SHALL provide following information to the congestion
manager as soon as the first packet on the fly was acknowledged by
any mean, or a legitimate packet falling in the receive window with
the ECE flag set is received:
- The local interface number that the packet carrying the ECE signal
is accepted.
- The remote network prefix that the congestion information is meant
to associate. Note that the aggregated host ID part is NOT included
in the prefix.
- The traffic class. For FSP it is bisected: MIND flag set or not.
- Number of outstanding octets, including all of those in the payload
AND the FSP headers.
- The effective round trip time calculated in the most recent period.
Note that retransmitted packets MUST be excluded on calculating the
effective RTT.
- Whether an ECN-Echo signal was received. The ECE flag of a
legitimate packet falling in the receive window is the ECN-Echo
signal.
- Whether a sent packet with SRR flag set is acknowledged.
The congestion manager SHOULD reduce the send rate if the FSP sender
informed it that an ECN-Echo signal was received.
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The sender SHALL NOT inform the congestion manager to reduce the send
rate again even if further packet with ECE flag set is received,
until at least one sent packet with SRR flag set is acknowledged.
A packet with ECE flag set received after the packet with SRR flag
set is acknowledged SHOULD make the congestion manager reduce the
send rate again.
Retransmitted packet SHALL be subjected to send rate control at the
underlying congestion management service sub-layer as well.
Quota or other means to enforce fairness among various FSP
connections SHOULD be provided directly to the ULA by the congestion
management service.
Requirement of an FSP congestion manager would be detailed in a
separate document.
8.8. On-the-Wire Compression
FSP exploits the lossless compression algorithm as per [LZ4].
If the CPR flag of the first packet of a transmit transaction is set,
compression is applied on the payload octet stream of the transaction
transaction.
When applying compression FSP divides source stream into multiple
blocks. For this version of FSP length of each block is 128KiB
(131072 octets), except the final block whose length may be less than
or equal to 128KiB. The final block is the one that terminate the
transmit transaction, i.e. which contains the last FSP packet of the
transmit transaction. The last FSP packet of the transmit transaction
has the EoT flag set. The "LZ4_compress_fast_continue" method SHALL
be applied on each block. That is, data from previous compressed
blocks are taken use for better compression ratio.
When transferring the result data of compressing each block, the
result data is prefixed with its length. The length is expressed by a
4-octets little-endian integer.
On-the-wire compression of each transmit transactions is independent.
It is the upper layer application that SHALL make agreement on which
transmit transaction utilizes on-the-wire compression.
8.9. Milk Like Payload and Minimal Delay Service
An ordinary data flow is wine-like in the sense that the older data
are more valuable. If it has to, data packet sent latest are dropped
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first. In the contrary, milk-like payload is that the newer data are
more precious and outdated data packet can be discarded.
When ULA is willing to accept incomplete message the peer of the
underling FSP node SHALL set the MIND flag of the first PERSIST
packet that starts the first transmit transaction, and set the MIND
flag of every following PURE_DATA packet, while set the Traffic Class
of the underlying IPv6 packet to some registered value.
In the transmission path, any relaying middle box, be it router or
switch, should reserve a reasonably short queue for the packet flow
of such flow to minimize delay.
When the receive buffer overflows the receiver discards the
undelivered packet received first to free buffer space for the latest
packet received. However it keeps order on delivering the packets to
he ULA. ULA may choose to discard packets received earlier than some
threshold.
The receiver SHOULD NOT make any acknowledgement to the packet
received with the MIND flag set.
Minimal delay service is asymmetric in the sense that one
transmission direction the data flow may be milk-like while in the
reverse direction the data flow may be wine-like.
A minimal delay service data flow is terminated by ULA via some out-
of-band control mechanism.
9. Graceful Shutdown
One participant of an FSP connection MAY initiate graceful shutdown
of the connection if and only if its peer has committed the most
recent transmit transaction.
By initiating graceful shutdown the participant tells its peer that
current transmit transaction is to be committed as well.
9.1. Initiation of Graceful Shutdown
(RELEASE, SN, ExpectedSN, ICC, FREWS)
An FSP end node MAY initiate graceful shutdown if it is in the
PEER_COMMIT, COMMITTING2 or CLOSABLE state. It SHALL NOT initiate
graceful shutdown if its peer has not committed current transmit
transaction.
Graceful shutdown is signaled to the remote end by sending a RELEASE
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command packet. The FSP end node SHALL migrate to the PRE_CLOSED
state just before sending the RELEASE packet.
9.2. Acknowledgment of Graceful Shutdown
The RELEASE packet may be accepted in the COMMITTING, COMMITTED,
COMMITTING2, CLOSABLE or PRE_CLOSED state.
If the legitimate RELEASE packet is received in the COMMITTING or
COMMITTED state, the FSP end node SHALL buffer the RELEASE packet,
wait each packet of the last transmit transaction of its peer has
been received, deliver all the buffered payload and then migrate to
the CLOSED state.
If the legitimate RELEASE packet is received in the COMMITTING2 or
CLOSABLE state, the FSP end node SHALL migrate to the CLOSED state
immediately.
In either of the two cases the receiver of the RELEASE packet SHALL
acknowledge the sender of the RELEASE packet with a legitimate out-
of-band ACK_FLUSH packet.
If the RELEASE packet is received in the PRE_CLOSED state, it is to
finalize the graceful shutdown procedure.
9.3. Finalization of Graceful Shutdown
If either the legitimate RELEASE packet or the legitimate ACK_FLUSH
packet is received in the PRE_CLOSED state the grace shutdown request
is supposed to be acknowledged and the shutdown procedure SHALL be
finalized by that the FSP end node migrates to the CLOSED state
immediately.
Graceful shutdown in FSP is asymmetric in the sense that it does not
require both ULA participants to call the Shutdown API.
9.4. Retransmission of RELEASE Packet
The FSP end node in the PRE_CLOSED state SHALL retransmit the RELEASE
packet until it migrates to CLOSED state or it is timed out. Interval
between the retransmission is hard-coded to 4 times of RTT.
The RELEASE packet that was sent in the COMMITTING2 or CLOSABLE state
state shall never be retransmitted.
10 Mobility and Multi-home Support
10.1. Heartbeat Signals
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FSP requires that the participants periodically send the heartbeat
signals.
The participant in the ACTIVE, COMMITTING, COMMITTED, PEER_COMMIT,
COMMITING2 or CLOSABLE state MUST send the KEEP_ ALIVE packet as the
heart-beat signal periodically to retain the connection in case that
underlying IP address has changed.
(KEEP_ALIVE, SN, ExpectedSN, ICC, FREWS, Sink Parameter, SNACK)
Heartbeat signal is an out-of-band control packet. It does not carry
payload. The sequence number of the KEEP_ALIVE packet SHALL be set to
the latest sequence number of all of the packets that have been sent.
Only the FSP node in the ACTIVE, COMMITTING, COMMITTED, PEER_COMMIT,
COMMITING2 or CLOSABLE state MAY process the heartbeat signal.
In this version of FSP the heat-beat period is arbitrarily set to 600
seconds.
The sequence number (SN) of the KEEP_ALIVE packet MUST equal the
latest sequence number of the legitimate packets that have been sent.
The out-of-band serial number SHALL increase by one whenever a new
KEEP_ALIVE packet is sent.
10.2. Active Address Change Signaling
During communication process the FSP participant whose underlying IP
address is changed SHOULD inform its peer such change by transmit a
KEEP_ALIVE packet with the Sink Parameter extension header and the
SNACK header so that the peer can retransmit the packets that were
negatively acknowledged.
Such informing KEEP_ALIVE packet SHALL be sent in the ACTIVE,
COMMITTING, COMMITTED, PEER_COMMIT, COMMITING2 or CLOSABLE state.
Informing KEEP_ALIVE packet SHOULD be sent more frequently than a
normal heart-beat signaling KEEP_ALIVE packet.
For this version of FSP informing KEEP_ALIVE packet SHALL be
retransmitted every 4 RTT interval until the heuristic
acknowledgement is received.
10.3. Heuristic Remote Address Change Adaptation
A participant of the FSP connection SHALL set the source address of
the packet to transmit or retransmit to new IP address as soon as the
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near-end IPv4 address or IPv6 network prefix has changed. The ULTID
field MUST remain the same.
When a new packet with a later sequence number is received and the
source IP address of the packet is found to be different with the
preserved IP address of the remote end, the receiver SHOULD
automatically update the preserved IP address of the remote end to
the source IP address of the new packet, unless there is a Sink
Parameter header in the packet.
If the sequence number of the packet received is not the latest in
the receive window the preserved IP address of the remote end SHALL
NOT be updated even if the source address of the received packet has
changed.
10.4. Heuristic Address Change Acknowledgement
The address change signaling KEEP_ALIVE packet is supposed to be
acknowledged if a packet targeted at the new IP address that the
KEEP_ALIVE packet has informed is received.
10.5. NAT-traversal and Multihoming
When FSP is implemented over UDP in the IPv4 network, each endpoint
of the FSP connection is bound one and only one IPv4 address as soon
as the connection is established. Each endpoint SHALL choose the
source IPv4 address of the last packet received as the destination
IPv4 address of the packet that it is to send later. By this mean FSP
over UDP is NAT-friendly.
When FSP is implemented over IPv6 as soon as the connection is
established the IPv6 address may be changed dynamically, and one more
alternate IP address may be added or removed dynamically for
individual endpoint as well, provided that ULTID part keeps unchanged
while the host IDs part of all IPv6 address of the endpoint are of
the same value at any given moment.
The sender may choose as the source IP address by selecting any
network prefix that it has most-recently sent to its peer in the
allowed address list field of the Sink Parameter header, joining with
the host ID in the Sink Parameter header and the stable ULTID of the
sender, and choose as the destination IP address by selecting any
network prefix in the allowed address list field of the Sink
Parameter header most-recently received from its peer, joining with
the peer's host ID and the peer's ULTID. Thus multiple multi-homed
paths MAY co-exist between the two FSP endpoints.
10.6. Explicit Multi-home Informing
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If an FSP end node is configured with multiple IPv4 address other
than the loop-back address, or with multiply global unicast IPv6
address, it MAY advertise multiple underlying addresses to the remote
end by put them in the addressable network prefix list of the Sink
Parameter extension header. The Sink Parameter extension header may
be carried in the CONNECT_REQUEST, ACK_CONNECT_REQ, NULCOMMIT,
MULTIPLY or KEEP_ALIVE packet.
Any participant of the communication SHALL NOT make discrimination of
the source or destination IP address of any packet provided that both
the source ULTID and the destination ULTID keep unchanged and the ICC
field passes verification.
11 Connection Multiplication
Connection multiplication is the process of incarnating a new
connection context by re-using security context of an established
connection.
11.1. Request to Multiply Connection
(MULTIPLY, SN, Salt, ICC, FREWS [, Sink Parameter] [, payload])
The initiator's initial sequence number of the new connection is the
sequence number of the packet that piggybacks the connection
multiplication header. The ExpectedSN field of the normal packet
store a Salt value instead.
The FREWS field MUST be processed in the new connection context while
the ICC MUST be calculated with the session key of the original
connection.
The new connection inherits the remaining key life. ULA SHOULD
negotiate new session key and/or install new session key as soon as
possible.
The optional payload of the MULTIPLY packet MUST be processed in the
new connection context.
The MULTIPLY packet is an out-of-band command packet in the original
connection context.
11.2. Response to Connection Multiplication Request
Case 1: (ACK_START, SN, ExpectedSN, ICC, FREWS [, Sink Parameter])
Case 2: (PERSIST, SN, ExpectedSN, ICC, FREWS, Payload)
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Case 3: (RESET, SN, ExpectedSN, ICC, FREWS, Reason of Failure)
In all of these cases the ULTID of the remote-end MUST be the value
of the initiator's ULTID in the connection multiplication header.
It is REQUIRED that only a connection in the ESTABLISHED, COMMITTING,
COMMITTED, PEER_COMMIT, COMMITTING2 or CLOSABLE state may accept a
connection multiplication request.
In case 1 the responder admits the multiplication request AND commit
the transmit transaction, the new connection enters into the
PEER_COMMIT or CLOSABLE state immediately, on request of ULA.
In case 2 the responder admits the multiplication request and the new
connection enters into the ESTABLISHED, PEER_COMMIT, or COMMITTING or
CLOSABLE state immediately, depending whether the ULA of the
multiplication initiator has requested to commit the transmit
transaction immediately and whether the ULA of the multiplication
responder has requested to commit the transmit transaction in the
reverse direction immediately.
In case 3 the responder rejects the multiplication request. To defend
against spoofing attack ICC MUST be valid. The value of the SN field
MUST equal the value of the 'Expected SN' field of the requesting
MULTIPLY packet while the value of ExpectedSN field MUST equal the
value of the 'Sequence No' field.
The new connection MUST derive new session key from the session key
of the original connection where the out-of-band requesting MULTIPLY
packet is received immediately.
11.3. Duplicate Detection of Connection Multiplication Request
Every time the responder of connection multiplication receives a
MULTIPLY packet it MUST check the suggested responder's ULTID and the
initiator's ULTID.
The responder MUST reject the multiplication request if the suggested
responder's ULTID equals the near-end ULTID of some connection and
the remote-end ULTID of that connection does not equal the
initiator's ULTID.
The responder MUST recognize the MULTIPLY packet as a duplicate
connection request if some connection matches the request and SHOULD
response by retransmitting the head packet of the send queue of the
matching connection, be it a PERSIST or an COMMIT packet. A
connection matches the MULTIPLY request if and only if the suggested
responder's ULTID in the MULTIPLY packet equals the near-end ULTID of
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the connection and the initiator's ULTID equals the remote-end ULTID
of the connection.
11.4. Retransmission
The initiating side SHALL retransmit the MULTIPLY packet if the
corresponding PERSIST packet is not received in some limit time (by
default 15 seconds).
11.5. Key Derivation for Branch Connection
Let K_out = BLAKE2(Km, [d] || Label || 0x00 || Context || L), where:
- Km
is the master key,
- [d]
is one octet of integer Depth. It is alike the KDF counter mode
as the NIST SP800-108. For this version of FSP it is the fixed
number 1,
- Label
is the fixed ASCII string "Multiply an FSP connection" which is
26-octet long for this version of FSP,
- Context
is concatenation of two 32-bit words idB and idR
idB is the ULTID allocated for the branch connection in the
context of the multiplication initiator. idB is byte-order
neutral.
idR is the receiver side ULTID of the original connection that is
to accept the connection multiplication request. idI or idR is
byte-order neutral.
- L
is a 32-bit network byte-order integer specifying the length in
bits of the derived key K-out
12 Timeouts and Abrupt Close
12.1. Timeouts in End-to-End Negotiation
Initially the initiator is in the CONNECT_BOOTSTRAP state. It
migrates to the CONNECT_ AFFIRMING state after it received the
legitimate ACK_INIT_CONNECT packet. Then it migrates to the
PEER_COMMIT or CLOSABLE state after it received the legitimate
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ACK_CONNECT _REQ packet, depending on the hint of ULA.
The responder incarnates a new connection context which is initially
in the CHALLENGING state after accepting a legitimate Connect Request
packet. Then it migrates to the COMMITTING or CLOSABLE state,
depending on the packet received from its peer.
If the initiator or the responder is unable to migrate to a new state
in some limit time (by default 60 seconds, except in LISTENING state)
it aborts the connection by recycling the connection context.
12.2. Timeouts in Multiply
Initially the initiating side of Connection Multiplication is in the
CLONING state. It migrates to the ACTIVE, COMMITTED, PEER_COMMIT or
CLOSABLE state after it received the legitimate PERSIST packet. Which
state to migrated depends on the EoT flag of the initiating MULTIPLY
packet and the responding PERSIST packet.
If the initiating side is unable to migrate to a new state in some
limit time (by default 60 seconds) it aborts multiplication by
recycling the new connection context.
12.3. Timeout of Transmit Transaction Commitment
The FSP node MUST abort the connection if the time of no packet
having arrived has exceed certain limit in the COMMITTING or
COMMITTING2 state.
In this FSP version, timeout of transmit transaction commitment is
set to 5 minutes.
12.4. Timeout of Graceful Shutdown
It simply migrates to the NON_EXISTENT pseudo-state if timeout in the
PRE_CLOSED state.
In this FSP version, timeout of Graceful Shutdown is set to 1 minute.
12.5. Idle Timeout
If one participant has not received any packet nor has it sent any
packet in some limit time, it MUST be abruptly closed.
In this FSP version the time limit, or the idle timeout, is set to 4
hours.
12.6. Session Key Timeout
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For this FSP version if a secret key is applied for more than 2^30
times the FSP node MUST abruptly closed instantly.
12.7. Abrupt Close
An FSP node abruptly shutdown a session by sending a RESET packet and
release all of the resource occupied by the the session immediately.
(RESET, SN, ExpectedSN, ICC, Reason of Failure)
13 Issues for Further Study
13.1. Resolution of ULTID in DNS
There are two patterns of IP address resolution in FSP: the DNS-
compatible pattern and the proxy pattern. The former pattern relies
on some name service to resolve the IP address of the responder for
the initiator before they exchange end-to-end negotiation packets.
In the DNS-compatible pattern, the responder side of the FSP
participants registered its address identifier, such as 'domain name'
in some name service such as DNS [RFC1034][RFC1035], according to
some pre-agreement at first. The initiator resolves the current IP
address of the responder by consulting the name service, such as
looking after the A or AAAA record [RFC3596] of the domain name in
DNS.
If UDP over IPv4 is exploited as the under layer data packet delivery
service the port number of the responder is firstly resolved just
alike normal network application such as HTTP. Then it is extended to
32-bit ULTID, and ULTIDs of FSP can be considered as the superset of
TCP port numbers.
If the string representation of IPv4/IPv6 address is applied directly
as the peer's address identifier instead of the domain name there is
no need for some real address resolution. But from the API caller's
point of view it is a DNS-compatible mode address resolution.
13.2. Proxy Pattern for Syndicated Name Resolution
The proxy pattern of IP address resolution in FSP is to embed the
address resolution information in the connection initialization
packets and is designed to work in FSP over IPv6 mode only.
In IPv6 network the rightmost 32 bits of the IPv6 address directly
maps to the ULTID so FSP does not need additional multiplexing
mechanism such as port number. And it needs not consult SRV record or
look for some entry in some 'services' file.
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If the INIT_CONNECT packet carries the responder's host name it MUST
take the link-local interface address as the source IPv6 address and
the default link-local gateway address, FE80::1, as the destination
IPv6 address no matter whether the global unicast IP address of the
default gateway is configured. In such scenario the link-local
gateway MUST be able to resolute the responder's host name to its
global unicast IPv6 address, and the gateway MUST be able to map the
initiator's link local address to its global unicast IPv6 address.
If the gateway that relays the INIT_CONNECT packet finds that the
responder is on the same link-local network with the initiator it
SHALL change the source and the destination IP addresses of the
INIT_CONNECT packet to the link-local IP addresses of the initiator
and the responder respectively, and relay the packet onto the same
link-local network.
On receiving the INIT_CONNECT packet that carries the responder's
host name the link-local gateway MUST resolute the responder's global
unicast IPv6 address and map the initiator's global unicast IPv6
address, and replace the destination and source address of the
INIT_CONNECT packet respectively, unless it finds that the initiator
and the responder are on the same link-local network, where the
gateway SHALL process the packet as stated in the previous statement.
13.3. Asymmetric Transmission
If there is one participant whose receive interface is not the same
as the send interface the participant is called an asymmetric-
transmissioned node.
Asymmetric transmission itself is asymmetric in the sense that one
participant may be asymmetric-transmissioned node while its peer is a
normal node that the send interface is the same receive interface.
An end node is asymmetric-transmissioned if it received an
ACK_CONNECT_REQ packet, NULCOMMIT or PERSIST packet whose source IP
address that the network interface accepting the packets reported is
not in the allowed IP address list in the Sink Parameter header of
the packet.
For an asymmetric-transmissioned remote end, the near end cannot rely
on automatic IP address change detection. Instead IP address change
notification mechanism shall be utilized.
However for this version of FSP asymmetric transmission support is
optional.
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14 Security Considerations
14.1. Deny of Service Attack
FSP is designed to mitigate effect of DoS attack by exploiting Cookie
.
However, resistance against distributed DoS attack relies on external
mechanism such as Distributed-Denial-of-Service Open Threat Signaling
[DOTS].
14.2. Replay Attack
In-band sequence number and out-of-band sequence number are exploited
to resist against replay attack.
14.3. Passive Attacks
AEAD MAY be exploited by the ULA to protect it against passive
attacks such as eavesdropping, gaining advantage by analyzing the
data sent.
MAC only service MAY also be utilized. Together with application
layer stream-mode encryption it protects the ULA against passive
attacks as well.
14.4. Masquerade Attack
Both AEAD and MAC only service may be exploited to protect the
endpoints against masquerade attack.
If proxy pattern for syndicated name resolution is exploited for FSP
over IPv6, secure neighbor discovery [RFC3971] SHOULD be applied
instead of common neighbor discovery whenever it is feasible.
14.5. Active Man-In-The-Middle Attack
The ULA SHALL take account to protect itself against MITM attack when
making client authentication and key establishment.
14.6. Privacy Concerns
It is beneficial for privacy protection that the ULTID of each
endpoints of an FSP connection is generated randomly [RFC7721].
15 IANA Considerations
It should be requested that the port number registered for UDP
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packets encapsulating FSP in the IPv4 network. The port number 18003
is exploited in the concept prototype implementation. The number is
the decimal presentation of ASCII codes of the character 'F' ('x46')
and 'S' ('x53') concatenated in network byte order.
It should be requested that the 'Next Header'/protocol number is
assigned for FSP over IPv6. Decimal number 144 is exploited in the
concept prototype implementation.
16 References
16.1. Normative References
[AES] NIST, "Advanced Encryption Standard (AES)", November 2001.
<https://doi.org/10.6028/NIST.FIPS.197>
[CRC64] ECMA, "Data Interchange on 12.7 mm 48-Track Magnetic Tape
Cartridges - DLT1 Format Standard, Annex B", ECMA-182,
December 1992.
[LZ4] https://lz4.github.io/lz4/
[GCM] NIST, "Recommendation for Block Cipher Modes of Operation:
Galois/Counter Mode (GCM) and GMAC", November 2007.
<http://dx.doi.org/10.6028/NIST.SP.800-38D>
[OSI/RM] ISO and IEC, "Information technology-Open Systems
Interconnection - Basic Reference Model: The Basic Model",
ISO/IEC 7498-1 Second edition, November 1994.
<https://www.iso.org/standard/20269.html>
[R01] Rogaway, P., "Authenticated encryption with Associated-
Data", ACM Conference on Computer and Communication
Security (CCS'02), pp. 98-107, ACM Press, 2002.
[RFC1122] Braden, R., Ed., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122, DOI
10.17487/RFC1122, October 1989, <https://www.rfc-
editor.org/info/rfc1122>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI
10.17487/RFC2119, March 1997, <https://www.rfc-
editor.org/info/rfc2119>.
[RFC3124] Balakrishnan, H. and S. Seshan, "The Congestion Manager",
RFC 3124, DOI 10.17487/RFC3124, June 2001,
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<https://www.rfc-editor.org/info/rfc3124>.
[RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
of Explicit Congestion Notification (ECN) to IP",
RFC 3168, DOI 10.17487/RFC3168, September 2001,
<https://www.rfc-editor.org/info/rfc3168>.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
2003, <https://www.rfc-editor.org/info/rfc3629>.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <https://www.rfc-editor.org/info/rfc4291>.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
December 2005, <https://www.rfc-editor.org/info/rfc4301>.
[RFC5869] Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand
Key Derivation Function (HKDF)", RFC 5869, DOI
10.17487/RFC5869, May 2010, <https://www.rfc-
editor.org/info/rfc5869>.
[RFC6887] Wing, D., Ed., Cheshire, S., Boucadair, M., Penno, R., and
P. Selkirk, "Port Control Protocol (PCP)", RFC 6887, DOI
10.17487/RFC6887, April 2013, <https://www.rfc-
editor.org/info/rfc6887>.
[RFC7693] Saarinen, M-J., Ed., and J-P. Aumasson, "The BLAKE2
Cryptographic Hash and Message Authentication Code (MAC)",
RFC 7693, DOI 10.17487/RFC7693, November 2015,
<https://www.rfc-editor.org/info/rfc7693>.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200, DOI
10.17487/RFC8200, July 2017, <https://www.rfc-
editor.org/info/rfc8200>.
[RFC8273] Brzozowski, J. and G. Van de Velde, "Unique IPv6 Prefix
per Host", RFC 8273, DOI 10.17487/RFC8273, December 2017,
<https://www.rfc-editor.org/info/rfc8273>.
[STD5] Postel, J., "Internet Protocol", STD 5, RFC 791, September
1981.
[STD6] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
August 1980.
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[STD7] Postel, J., "Transmission Control Protocol", STD 7, RFC
793, September 1981.
16.2. Informative References
[DOTS] Mortensen, A., Andreasen, F., Reddy, T., Gray, C., Compton
R., and N. Teague, "Distributed-Denial-of-Service Open
Threat Signaling (DOTS) Architecture", March 2018,
<https://datatracker.ietf.org/doc/draft-ietf-dots-
architecture/>
[Gao2002] Gao, J., "Fuzzy-layering and its suggestion", IETF Mail
Archive, September 2002,
https://mailarchive.ietf.org/arch/msg/ietf/u-6i-6f-
Etuvh80-SUuRbSCDTwg
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<https://www.rfc-editor.org/info/rfc1034>.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/info/rfc1035>.
[RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network
Address Translator (Traditional NAT)", RFC 3022, DOI
10.17487/RFC3022, January 2001, <https://www.rfc-
editor.org/info/rfc3022>.
[RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,
C., and M. Carney, "Dynamic Host Configuration Protocol
for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July
2003, <https://www.rfc-editor.org/info/rfc3315>.
[RFC3596] Thomson, S., Huitema, C., Ksinant, V., and M. Souissi,
"DNS Extensions to Support IP Version 6", STD 88,
RFC 3596, DOI 10.17487/RFC3596, October 2003,
<https://www.rfc-editor.org/info/rfc3596>.
[RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
Host Configuration Protocol (DHCP) version 6", RFC 3633,
DOI 10.17487/RFC3633, December 2003, <https://www.rfc-
editor.org/info/rfc3633>.
[RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
"SEcure Neighbor Discovery (SEND)", RFC 3971, DOI
10.17487/RFC3971, March 2005, <https://www.rfc-
editor.org/info/rfc3971>.
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[RFC4086] Eastlake 3rd, D., Schiller, J., and S. Crocker,
"Randomness Requirements for Security", BCP 106, RFC 4086,
DOI 10.17487/RFC4086, June 2005, <https://www.rfc-
editor.org/info/rfc4086>.
[RFC4106] Viega, J. and D. McGrew, "The Use of Galois/Counter Mode
(GCM) in IPsec Encapsulating Security Payload (ESP)",
RFC 4106, DOI 10.17487/RFC4106, June 2005,
<https://www.rfc-editor.org/info/rfc4106>.
[RFC4555] Eronen, P., "IKEv2 Mobility and Multihoming Protocol
(MOBIKE)", RFC 4555, DOI 10.17487/RFC4555, June 2006,
<https://www.rfc-editor.org/info/rfc4555>.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
DOI 10.17487/RFC4861, September 2007, <https://www.rfc-
editor.org/info/rfc4861>.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862, DOI
10.17487/RFC4862, September 2007, <https://www.rfc-
editor.org/info/rfc4862>.
[RFC5072] Varada, S., Ed., Haskins, D., and E. Allen, "IP Version 6
over PPP", RFC 5072, DOI 10.17487/RFC5072, September 2007,
<https://www.rfc-editor.org/info/rfc5072>.
[RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated
Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008,
<https://www.rfc-editor.org/info/rfc5116>.
[RFC5942] Singh, H., Beebee, W., and E. Nordmark, "IPv6 Subnet
Model: The Relationship between Links and Subnet
Prefixes", RFC 5942, DOI 10.17487/RFC5942, July 2010,
<https://www.rfc-editor.org/info/rfc5942>.
[RFC6059] Krishnan, S. and G. Daley, "Simple Procedures for
Detecting Network Attachment in IPv6", RFC 6059, DOI
10.17487/RFC6059, November 2010, <https://www.rfc-
editor.org/info/rfc6059>.
[RFC6177] Narten, T., Huston, G., and L. Roberts, "IPv6 Address
Assignment to End Sites", BCP 157, RFC 6177, DOI
10.17487/RFC6177, March 2011, <https://www.rfc-
editor.org/info/rfc6177>.
[RFC6434] Jankiewicz, E., Loughney, J., and T. Narten, "IPv6 Node
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Requirements", RFC 6434, DOI 10.17487/RFC6434, December
2011, <https://www.rfc-editor.org/info/rfc6434>.
[RFC7050] Savolainen, T., Korhonen, J., and D. Wing, "Discovery of
the IPv6 Prefix Used for IPv6 Address Synthesis",
RFC 7050, DOI 10.17487/RFC7050, November 2013,
<https://www.rfc-editor.org/info/rfc7050>.
[RFC7157] Troan, O., Ed., Miles, D., Matsushima, S., Okimoto, T.,
and D. Wing, "IPv6 Multihoming without Network Address
Translation", RFC 7157, DOI 10.17487/RFC7157, March 2014,
<https://www.rfc-editor.org/info/rfc7157>.
[RFC7323] Borman, D., Braden, B., Jacobson, V., and R.
Scheffenegger, Ed., "TCP Extensions for High Performance",
RFC 7323, DOI 10.17487/RFC7323, September 2014,
<https://www.rfc-editor.org/info/rfc7323>.
[RFC7608] Boucadair, M., Petrescu, A., and F. Baker, "IPv6 Prefix
Length Recommendation for Forwarding", BCP 198, RFC 7608,
DOI 10.17487/RFC7608, July 2015, <https://www.rfc-
editor.org/info/rfc7608>.
[RFC7721] Cooper, A., Gont, F., and D. Thaler, "Security and Privacy
Considerations for IPv6 Address Generation Mechanisms",
RFC 7721, DOI 10.17487/RFC7721, March 2016,
<https://www.rfc-editor.org/info/rfc7721>.
[RFC8084] Fairhurst, G., "Network Transport Circuit Breakers",
BCP 208, RFC 8084, DOI 10.17487/RFC8084, March 2017,
<https://www.rfc-editor.org/info/rfc8084>.
[RFC8085] Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage
Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085,
March 2017, <https://www.rfc-editor.org/info/rfc8085>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8170] Thaler, D., Ed., "Planning for Protocol Adoption and
Subsequent Transitions", RFC 8170, DOI 10.17487/RFC8170,
May 2017, <https://www.rfc-editor.org/info/rfc8170>.
[tcpcrypt] Bittau, A., Hamburg, M., Handley, M., Mazieres, D., and D.
Boneh, "The case for ubiquitous transport-level
encryption", USENIX Security , 2010.
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17 Acknowledgements
Authors' Addresses
Jun'an Gao
Beijing Static Traffic Investment and Operation Co.,Ltd.
Shouke Plaza-A, Liuliqiao South, Fengtai
Beijing
People's Republic of China
EMail: jagao@outlook.com
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