SCTP-Based Transport Mapping Layer (TML) for the Forwarding and Control Element Separation (ForCES) Protocol
draft-ietf-forces-sctptml-08
The information below is for an old version of the document that is already published as an RFC.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 5811.
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|---|---|---|---|
| Authors | Kentaro Ogawa , Jamal Hadi Salim | ||
| Last updated | 2015-10-14 (Latest revision 2010-01-19) | ||
| Replaces | draft-hadi-forces-sctptml | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | Proposed Standard | ||
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draft-ietf-forces-sctptml-08
Network Working Group J. Hadi Salim
Internet-Draft Mojatatu Networks
Intended status: Standards Track K. Ogawa
Expires: July 23, 2010 NTT Corporation
January 19, 2010
SCTP based TML (Transport Mapping Layer) for ForCES protocol
draft-ietf-forces-sctptml-08
Abstract
This document defines the SCTP based TML (Transport Mapping Layer)
for the ForCES protocol. It explains the rationale for choosing the
SCTP (Stream Control Transmission Protocol) and also describes how
this TML addresses all the requirements required by and the ForCES
protocol.
Status of this Memo
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Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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Table of Contents
1. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Protocol Framework Overview . . . . . . . . . . . . . . . . . 4
3.1. The PL . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.2. The TML . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.2.1. TML and PL Interfaces . . . . . . . . . . . . . . . . 6
3.2.2. TML Parameterization . . . . . . . . . . . . . . . . . 7
4. SCTP TML overview . . . . . . . . . . . . . . . . . . . . . . 8
4.1. Rationale for using SCTP for TML . . . . . . . . . . . . . 8
4.2. Meeting TML requirements . . . . . . . . . . . . . . . . . 9
4.2.1. SCTP TML Channels . . . . . . . . . . . . . . . . . . 10
4.2.2. Satisfying TML Requirements . . . . . . . . . . . . . 15
5. SCTP TML Channel Work . . . . . . . . . . . . . . . . . . . . 17
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
7. Security Considerations . . . . . . . . . . . . . . . . . . . 18
7.1. IPsec Usage . . . . . . . . . . . . . . . . . . . . . . . 19
7.1.1. SAD and SPD setup . . . . . . . . . . . . . . . . . . 19
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 19
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
9.1. Normative References . . . . . . . . . . . . . . . . . . . 20
9.2. Informative References . . . . . . . . . . . . . . . . . . 20
Appendix A. Suggested SCTP TML Channel Work Implementation . . . 21
A.1. SCTP TML Channel Initialization . . . . . . . . . . . . . 21
A.2. Channel work scheduling . . . . . . . . . . . . . . . . . 22
A.2.1. FE Channel work scheduling . . . . . . . . . . . . . . 22
A.2.2. CE Channel work scheduling . . . . . . . . . . . . . . 22
A.3. SCTP TML Channel Termination . . . . . . . . . . . . . . . 23
A.4. SCTP TML NE level channel scheduling . . . . . . . . . . . 24
Appendix B. Suggested Service Interface . . . . . . . . . . . . . 24
B.1. TML Boot-strapping . . . . . . . . . . . . . . . . . . . . 25
B.2. TML Shutdown . . . . . . . . . . . . . . . . . . . . . . . 26
B.3. TML Sending and Receiving . . . . . . . . . . . . . . . . 27
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 29
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1. Definitions
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.
The following definitions are taken from [RFC3654]and [RFC3746]:
Logical Functional Block (LFB) -- A template that represents a fine-
grained, logically separate aspects of FE processing.
ForCES Protocol -- The protocol used at the Fp reference point in the
ForCES Framework in [RFC3746].
ForCES Protocol Layer (ForCES PL) -- A layer in the ForCES
architecture that embodies the ForCES protocol and the state transfer
mechanisms as defined in [I-D.ietf-forces-protocol].
ForCES Protocol Transport Mapping Layer (ForCES TML) -- A layer in
ForCES protocol architecture that specifically addresses the protocol
message transportation issues, such as how the protocol messages are
mapped to different transport media (like SCTP, IP, TCP, UDP, ATM,
Ethernet, etc), and how to achieve and implement reliability,
security, etc.
2. Introduction
The ForCES (Forwarding and Control Element Separation) working group
in the IETF defines the architecture and protocol for separation of
Control Elements(CE) and Forwarding Elements(FE) in Network
Elements(NE) such as routers. [RFC3654] and [RFC3746] respectively
define architectural and protocol requirements for the communication
between CE and FE. The ForCES protocol layer specification
[I-D.ietf-forces-protocol] describes the protocol semantics and
workings. The ForCES protocol layer operates on top of an inter-
connect hiding layer known as the TML. The relationship is
illustrated in Figure 1.
This document defines the SCTP based TML for the ForCES protocol
layer. It also addresses all the requirements for the TML including
security, reliability, etc as defined in [I-D.ietf-forces-protocol].
3. Protocol Framework Overview
The reader is referred to the Framework document [RFC3746], and in
particular sections 3 and 4, for an architectural overview and
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explanation of where and how the ForCES protocol fits in.
There is some content overlap between the ForCES protocol
specification [I-D.ietf-forces-protocol] and this section (Section 3)
in order to provide basic context to the reader of this document.
The ForCES protocol layering constitutes two pieces: the PL and TML.
This is depicted in Figure 1.
+----------------------------------------------+
| CE PL |
+----------------------------------------------+
| CE TML |
+----------------------------------------------+
^
|
ForCES PL |messages
|
v
+-----------------------------------------------+
| FE TML |
+-----------------------------------------------+
| FE PL |
+-----------------------------------------------+
Figure 1: Message exchange between CE and FE to establish an NE
association
The PL is in charge of the ForCES protocol. Its semantics and
message layout are defined in [I-D.ietf-forces-protocol]. The TML is
necessary to connect two ForCES end-points as shown in Figure 1.
Both the PL and TML are standardized by the IETF. While only one PL
is defined, different TMLs are expected to be standardized. The TML
at each of the nodes (CE and FE) is expected to be of the same
definition in order to inter-operate.
When transmitting from a ForCES end-point, the PL delivers its
messages to the TML. The TML then delivers the PL message to the
destination TML(s).
On reception of a message, the TML delivers the message to its
destination PL (as described in the ForCES header).
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3.1. The PL
The PL is common to all implementations of ForCES and is standardized
by the IETF [I-D.ietf-forces-protocol]. The PL is responsible for
associating an FE or CE to an NE. It is also responsible for tearing
down such associations.
An FE may use the PL to asynchronously send packets to the CE. The
FE may redirect via the PL (from outside the NE) various control
protocol packets (e.g. OSPF, etc) to the CE. Additionally, the FE
delivers various events that CE has subscribed-to via PL
[I-D.ietf-forces-model].
The CE and FE may interact synchronously via the PL. The CE issues
status requests to the FE and receives responses via the PL. The CE
also configures the associated FE's LFBs' components using the PL
[I-D.ietf-forces-model].
3.2. The TML
The TML is responsible for transport of the PL messages.
[I-D.ietf-forces-protocol] section 5 defines the requirements that
need to be met by a TML specification. The SCTP TML specified in
this document meets all the requirements specified in
[I-D.ietf-forces-protocol] section 5. Section 4.2.2 describes how
the TML requirements are met.
3.2.1. TML and PL Interfaces
There are two interfaces to the PL and TML. The specification of
these interfaces is out of scope for this document, but the
interfaces are introduced to show how they fit into the architecture
and summarize the function provided at the interfaces. The first
interface is between the PL and TML and the other is the CE Manager
(CEM)/FE Manager (FEM)[RFC3746] interface to both the PL and TML.
Both interfaces are shown in Figure 2.
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+----------------------------+
| +----------------------+ |
| | | |
+---------+ | | PL | |
| | | +----------------------+ |
|FEM/CEM |<---->| ^ |
| | | | |
+---------+ | |TML API |
| | |
| V |
| +----------------------+ |
| | | |
| | TML | |
| | | |
| +----------------------+ |
+----------------------------+
Figure 2: The TML-PL interface
The CEM/FEM[RFC3746] interface is responsible for bootstrapping and
parameterization of the TML. In its most basic form the CEM/FEM
interface takes the form of a simple static config file which is read
on startup in the pre-association phase.
Appendix B discusses in more details the service interfaces.
3.2.2. TML Parameterization
It is expected that it should be possible to use a configuration
reference point, such as the FEM or the CEM, to configure the TML.
Some of the configured parameters may include:
o PL ID
o Connection Type and associated data. For example if a TML uses
IP/SCTP then parameters such as SCTP ports and IP addresses need
to be configured.
o Number of transport connections
o Connection Capability, such as bandwidth, etc.
o Allowed/Supported Connection QoS policy (or Congestion Control
Policy)
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4. SCTP TML overview
SCTP [RFC4960] is an end-to-end transport protocol that is equivalent
to TCP, UDP, or DCCP in many aspects. With a few exceptions, SCTP
can do most of what UDP, TCP, or DCCP can achieve. SCTP as well can
do most of what a combination of the other transport protocols can
achieve (e.g. TCP and DCCP or TCP and UDP).
Like TCP, it provides ordered, reliable, connection-oriented, flow-
controlled, congestion controlled data exchange. Unlike TCP, it does
not provide byte streaming and instead provides message boundaries.
Like UDP, it can provide unreliable, unordered data exchange. Unlike
UDP, it does not provide multicast support
Like DCCP, it can provide unreliable, ordered, congestion controlled,
connection-oriented data exchange.
SCTP also provides other services that none of the 3 transport
protocols mentioned above provide that we found attractive. These
include:
o Multi-homing
o Runtime IP address binding
o A range of reliability shades with congestion control
o Built-in heartbeats
o Multi-streaming
o Message boundaries with reliability
o Improved SYN DOS protection
o Simpler transport events
o Simplified replicasting
4.1. Rationale for using SCTP for TML
SCTP has all the features required to provide a robust TML. As a
transport that is all-encompassing, it negates the need for having
multiple transport protocols in order to satisfy the TML requirements
([I-D.ietf-forces-protocol] section 5). As a result it allows for
simpler coding and therefore reduces a lot of the interoperability
concerns.
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SCTP is also very mature and widely used, making it a good choice for
ubiquitous deployment.
4.2. Meeting TML requirements
PL
+----------------------+
| |
+-----------+----------+
| TML API
TML |
+-----------+----------+
| | |
| +------+------+ |
| | TML core | |
| +-+----+----+-+ |
| | | | |
| SCTP socket API |
| | | | |
| | | | |
| +-+----+----+-+ |
| | SCTP | |
| +------+------+ |
| | |
| | |
| +------+------+ |
| | IP | |
| +-------------+ |
+----------------------+
Figure 3: The TML-SCTP interface
Figure 3 details the interfacing between the PL and SCTP TML and the
internals of the SCTP TML. The core of the TML interacts on its
north-bound interface to the PL (utilizing the TML API). On the
south-bound interface, the TML core interfaces to the SCTP layer
utilizing the standard socket interface[I-D.ietf-tsvwg-sctpsocket].
There are three SCTP socket connections opened between any two PL
endpoints (whether FE or CE).
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4.2.1. SCTP TML Channels
+--------------------+
| |
| TML core |
| |
+-+-------+--------+-+
| | |
| Med prio, |
| Semi-reliable |
| channel |
| | Low prio,
| | Unreliable
| | channel
| | |
^ ^ ^
| | |
Y Y Y
High prio,| | |
reliable | | |
channel | | |
Y Y Y
+-+--------+--------+-+
| |
| SCTP |
| |
+---------------------+
Figure 4: The TML-SCTP channels
Figure 4 details further the interfacing between the TML core and
SCTP layers. There are 3 channels used to group and prioritize the
work for different types of ForCES traffic. Each channel constitutes
an SCTP socket interface which has different properties. It should
be noted that all SCTP channels are congestion aware (and for that
reason that detail is left out of the description of the 3 channels).
SCTP port 6704, 6705, 6706 are used for the higher, medium and lower
priority channels respectively. SCTP Payload Protocol ID (PPID)
values of 21, 22, and 23 are used for the higher, medium and lower
priority channels respectively.
4.2.1.1. Justifying Choice of 3 Sockets
SCTP allows up to 64K streams to be sent over a single socket
interface. The authors initially envisioned using a single socket
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for all three channels (mapping a channel to an SCTP stream). This
simplifies programming of the TML as well as conserves use of SCTP
ports.
Further analysis revealed head of line blocking issues with this
initial approach. Lower priority packets not needing reliable
delivery could block higher priority packets (needing reliable
delivery) under congestion situation for an indeterminate period of
time (depending on how many outstanding lower priority packets are
pending). For this reason, we elected to go with mapping each of the
three channels to a different SCTP socket (instead of a different
stream within a single socket).
4.2.1.2. Higher Priority, Reliable channel
The higher priority (HP) channel uses a standard SCTP reliable socket
on port 6704. SCTP PPID 21 is used for all messages on the HP
channel. The HP channel is used for CE solicited messages and their
responses:
1. ForCES configuration messages flowing from CE to FE and responses
from the FE to CE.
2. ForCES query messages flowing from CE to FE and responses from
the FE to the CE.
PL priorities 4-7 MUST be used for all PL messages using this
channel. The following PL messages MUST use the HP channel for
transport:
o Association Setup (default priority: 7)
o Association Setup Response (default priority: 7)
o Association Teardown (default priority: 7)
o Config (default priority: 4)
o Config Response (default priority: 4)
o Query (default priority: 4)
o Query Response (default priority: 4)
If PL priorities outside of the specified range (4-7) priority, PPID
or PL message types other than the above are received on the HP
channel, then the PL message MUST be dropped.
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Although an implementation may choose different values from the
defined range (4-7), it is RECOMMENDED that default priorities be
used. A response to a ForCES message MUST contain the same priority
as the request. Example, a config sent by the CE with priority 5
MUST have a config-response from the FE with priority 5.
4.2.1.3. Medium Priority, Semi-Reliable channel
The medium priority (MP) channel uses SCTP-PR on port 6705. SCTP
PPID 22 MUST be used for all messages on the MP channel. Time limits
on how long a message is valid are set on each outgoing message.
This channel is used for events from the FE to the CE that are
obsoleted over time. Events that are accumulative in nature and are
recoverable by the CE (by issuing a query to the FE) can tolerate
lost events and therefore should use this channel. For example, a
generated event which carries the value of a counter that is
monotonically incrementing fits to use this channel.
PL priority 3 MUST be used for PL messages on this channel. The
following PL messages MUST use the MP channel for transport:
o Event Notification (default priority: 3)
If PL priority outside of the specified priority, PPID or PL message
type other than the above are received on the MP channel, then the PL
message MUST be dropped.
4.2.1.4. Lower Priority, Unreliable channel
The lower priority (LP) channel uses SCTP port 6706. SCTP PPID 23 is
used for all messages on the LP channel. The LP channel also MUST
use SCTP-PR with lower timeout values than the MP channel. The
reason an unreliable channel is used for redirect messages is to
allow the control protocol at both the CE and its peer-endpoint to
take charge of how the end-to-end semantics of the said control
protocol's operations. For example:
1. Some control protocols are reliable in nature, therefore making
this channel reliable introduces an extra layer of reliability
which could be harmful. So any end-to-end retransmits will
happen from remote.
2. Some control protocols may desire to have obsolescence of
messages over retransmissions; making this channel reliable
contradicts that desire.
Given ForCES PL heartbeats are traffic sensitive, sending them over
the LP channel also makes sense. If the other end is not processing
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other channels it will eventually get heartbeats; and if it is busy
processing other channels heartbeats will be obsoleted locally over
time (and it does not matter if they did not make it).
PL priorities 1-2 MUST be used for PL messages on this channel. PL
messages that MUST use the MP channel for transport are:
o Packet Redirect (default priority: 2)
o Heartbeats (default priority: 1)
If PL priorities outside of the specified priority range, PPID or PL
message types other than the above are received on the LP channel,
then the PL message MUST be dropped.
4.2.1.5. Scheduling of The 3 Channels
Strict priority work-conserving scheduling is used to process both on
sending and receiving (of the PL messages) by the TML Core as shown
in Figure 5.
This means that the HP messages are always processed first until
there are no more left. The LP channel is processed only if channels
that are a higher priority than itself has no more messages left to
process. This means that under congestion situation, a higher
priority channel with sufficient messages that occupy the available
bandwidth would starve lower priority channel(s).
The design intent of the SCTP TML is to tie processing prioritization
as described in Section 4.2.1.1 and transport congestion control to
provide implicit node congestion control. This is further detailed
in Appendix A.2.
It should be emphasized that the work scheduling prioritization
scheme prescribed in this document is receiver based processing.
Fully arrived packets on any of the channels are a source of work
whose output may result in transmitted packets. However, we have no
control on the order in which SCTP/OS/network chooses to send
transmitted packets across and make them available to the receiver.
This is a limitation that we try to ameliorate by our choice of
channel properties, ForCES message grouping and the tying of CE and
FE work scheduling. And while that helps us ameliorate some of these
issues it does not fully resolve all.
From a ForCES perspective, we can tolerate some reordering. Example:
If an FE transmits a config response (HP), followed by 10000 OSPF
redirect packets(LP) and the CE gets 5 OSPF redirects (LP) first
before the config response(HP), that is tolerable. What matters is
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the CE gets to processing the HP message soon (instead of sitting in
long periods of time processing OSPF packets which would have
happened if we use a single socket with 3 streams). This is
particularly important in order to deal well with node overload as
discussed in Section 4.2.2.6.
SCTP channel +----------+
Work available | DONE +---<--<--+
| +---+------+ |
Y ^
| +-->--+ +-->---+ |
+-->-->-+ | | | | |
| | | | | | ^
| ^ ^ Y ^ Y |
^ / \ | | | | |
| / \ | ^ | ^ ^
| / Is \ | / \ | / \ |
| / there \ | /Is \ | /Is \ |
^ / HP work \ ^ /there\ ^ /there\ ^
| \ ? / | /MP work\ | /LP work\ |
| \ / | \ ? / | \ ? / |
| \ / | \ / | \ / ^
| \ / ^ \ / ^ \ / |
| \ / | \ / | \ / |
^ Y-->-->-->+ Y-->-->-->+ Y->->->-+
| | NO | NO | NO
| | | |
| Y Y Y
| | YES | YES | YES
^ | | |
| Y Y Y
| +----+------+ +---|-------+ +----|------+
| |- process | |- process | |- process |
| | HP work | | MP work | | LP work |
| +------+----+ +-----+-----+ +-----+-----+
| | | |
^ Y Y Y
| | | |
| Y Y Y
+--<--<---+--<--<----<----+-----<---<-----+
Figure 5: SCTP TML Strict Priority Scheduling
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4.2.1.6. SCTP TML Parameterization
The following is a list of parameters needed for booting the TML. It
is expected these parameters will be extracted via the FEM/CEM
interface for each PL ID.
1. The IP address(es) or a resolvable DNS/hostname(s) of the CE/FE.
2. Whether to use IPsec or not. If IPsec is used, how to
parameterize the different required ciphers, keys etc as
described in Section 7.1
3. The HP SCTP port, as discussed in Section 4.2.1.2. The default
HP port value is 6704 (Section 6).
4. The MP SCTP port, as discussed in Section 4.2.1.3. The default
MP port value is 6705 (Section 6).
5. The LP SCTP port, as discussed in Section 4.2.1.4. The default
LP port value is 6706 (Section 6).
4.2.2. Satisfying TML Requirements
[I-D.ietf-forces-protocol] section 5 lists requirements that a TML
needs to meet. This section describes how the SCTP TML satisfies
those requirements.
4.2.2.1. Satisfying Reliability Requirement
As mentioned earlier, a shade of reliability ranges is possible in
SCTP. Therefore this requirement is met.
4.2.2.2. Satisfying Congestion Control Requirement
Congestion control is built into SCTP. Therefore, this requirement
is met.
4.2.2.3. Satisfying Timeliness and Prioritization Requirement
By using 3 sockets in conjunction with the partial-reliability
feature[RFC3758], both timeliness and prioritization requirements are
addressed.
4.2.2.4. Satisfying Addressing Requirement
There are no extra headers required for SCTP to fulfil this
requirement. SCTP can be told to replicast packets to multiple
destinations. The TML implementation will need to translate PL
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addresses, to a variety of unicast IP addresses in order to emulate
multicast and broadcast PL addresses.
4.2.2.5. Satisfying High Availability Requirement
Transport link resiliency is one of SCTP's strongest point. Failure
detection and recovery is built in, as mentioned earlier.
o The SCTP multi-homing feature is used to provide path diversity.
Should one of the peer IP addresses become unreachable, the
other(s) are used without needing lower layer convergence
(routing, for example) or even the TML becoming aware.
o SCTP heartbeats and data transmission thresholds are used on a per
peer IP address to detect reachability faults. The faults could
be a result of an unreachable address or peer, which may be caused
by a variety of reasons, like interface, network, or endpoint
failures. The cause of the fault is noted.
o With the ADDIP feature, one can migrate IP addresses to other
nodes at runtime. This is not unlike the VRRP[RFC3768] protocol
use. This feature is used in addition to multi-homing in a
planned migration of activity from one FE/CE to another. In such
a case, part of the provisioning recipe at the CE for replacing an
FE involves migrating activity of one FE to another.
4.2.2.6. Satisfying Node Overload Prevention Requirement
The architecture of this TML defines three separate channels, one per
socket, to be used within any FE-CE setup. The work scheduling
design for processing the TML channels (Section 4.2.1.5) is strict
priority. A fundamental desire of the strict prioritization is to
ensure that more important processing work always gets node resources
over lesser important work.
When a ForCES node CPU is overwhelmed because the incoming packet
rate is higher than it can keep up with, the channel queues grow and
transport congestion subsequently follows. By virtue of using SCTP,
the congestion is propagated back to the source of the incoming
packets and eventually alleviated.
The HP channel work gets prioritized at the expense of the MP which
gets prioritized over LP channels. The preferential scheduling only
kicks in when there is node overload regardless of whether there is
transport congestion. As a result of the preferential work
treatment, the ForCES node achieves a robust steady processing
capacity. Refer to Appendix A.2 for details on scheduling.
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For an example of how the overload prevention works: consider a
scenario where an overwhelming amount redirected packets (from
outside the NE) coming into the NE may overload the FE while it has
outstanding config work from the CE. In such a case, the FE, while
it is busy processing config requests from the CE essentially ignores
processing the redirect packets on the LP channel. If enough
redirect packets accumulate, they are dropped either because the LP
channel threshold is exceeded or because they are obsoleted. If on
the other hand, the FE has successfully processed the higher priority
channels and their related work, then it can proceed and process the
LP channel. So as demonstrated in this case, the TML ties transport
congestion and node overload implicitly together.
4.2.2.7. Satisfying Encapsulation Requirement
The SCTP TML sets SCTP PPIDs to identify channels used as described
in Section 4.2.1.1.
5. SCTP TML Channel Work
There are two levels of TML channel work within an NE when a ForCES
node (CE or FE) is connected to multiple other ForCES nodes:
1. NE-level I/O work where a ForCES node (CE or FE) needs to choose
which of the peer nodes to process.
2. Node-level I/O work where a ForCES node, handles the three SCTP
TML channels separately for each single ForCES endpoint.
NE-level scheduling definition is left up to the implementation and
is considered out of scope for this document. Appendix A.4 discuss
briefly some constraints that an implementer needs to worry about.
This document provides suggestions on SCTP channel work
implementation in Appendix A.
The FE SHOULD do channel connections to the CE in the order of
incrementing priorities i.e. LP socket first, followed by MP and
ending with HP socket connection. The CE, however, MUST NOT assume
that there is ordering of socket connections from any FE.
6. IANA Considerations
Following the policies outlined in "Guidelines for Writing an IANA
Considerations Section in RFCs" [RFC5226], the following name spaces
are defined in ForCES SCTP TML.
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o SCTP port 6704 for the HP channel, 6705 for the MP channel, and
6706 for the LP channel.
o SCTP Payload Protocol ID (PPID) 21 for the HP channel, 22 for the
MP channel, and 23 for the LP channel.
XXX [Note to IANA]: Port allocations(SCTP 6700-6702) were made in
August 2009. We have been asked by IESG to change these as
prescribed above.
7. Security Considerations
The SCTP TML provides the following security services to the PL:
o A mechanism to authenticate ForCES CEs and FEs at transport level
in order to prevent the participation of unauthorized CEs and
unauthorized FEs in the control and data path processing of a
ForCES NE.
o A mechanism to ensure message authentication of PL data and
headers transferred from the CE to FE (and vice-versa) in order to
prevent the injection of incorrect data into PL messages.
o A mechanism to ensure the confidentiality of PL data and headers
transferred from the CE to FE (and vice-versa), in order to
prevent disclosure of PL information transported via the TML.
Security choices provided by the TML are made by the operator and
take effect during the pre-association phase of the ForCES protocol.
An operator may choose to use all, some or none of the security
services provided by the TML in a CE-FE connection.
When operating under a secured environment, or for other operational
concerns (in some cases performance issues) the operator may turn off
all the security functions between CE and FE.
IP Security Protocol (IPsec) [RFC4301] is used to provide needed
security mechanisms.
IPsec is an IP level security scheme transparent to the higher-layer
applications and therefore can provide security for any transport
layer protocol. This gives IPsec the advantage that it can be used
to secure everything between the CE and FE without expecting the TML
implementation to be aware of the details.
The IPsec architecture is designed to provide message integrity and
message confidentiality outlined in the TML security requirements
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[I-D.ietf-forces-protocol]. Mutual authentication and key exchange
protocol are provided by Internet Key Exchange (IKE)[RFC2409].
7.1. IPsec Usage
A ForCES FE or CE MUST support the following:
o Internet Key Exchange (IKE)[RFC2409] with certificates for
endpoint authentication.
o Transport Mode Encapsulating Security Payload (ESP)[RFC4303].
o HMAC-SHA1-96 [RFC2404] for message integrity protection
o AES-CBC with 128-bit keys [RFC3602] for message confidentiality.
o Replay protection[RFC4301].
A compliant implementation SHOULD provide operational means for
configuring the CE and FE to negotiate other cipher suites and even
use manual keying.
7.1.1. SAD and SPD setup
To minimize the operational configuration it is RECOMMENDED that only
the IANA issued SCTP protocol number(132) be used as a selector in
the Security Policy Database (SPD) for ForCES. In such a case only a
single SPD and SAD entry is needed.
Setup MAY alternatively extend the above policy so that it uses the 3
SCTP TML port numbers as SPD selectors. But as noted above this
choice will require increased number of SPD entries.
In scenarios where multiple IP addresses are used within a single
association, and there is desire to configure different policies on a
per IP address, then it is RECOMMENDED to follow [RFC3554]
8. Acknowledgements
The authors would like to thank Joel Halpern, Michael Tuxen, Randy
Stewart, Evangelos Haleplidis, Chuanhuang Li, Lars Eggert, Avshalom
Houri, Adrian Farrel, Juergen Quittek, Magnus Westerlund, and Pasi
Eronen for engaging us in discussions that have made this document
better.
Ross Callon was an excellent manager who persevered in providing us
guidance and Joel Halpern was an excellent document shepherd without
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whom this document would have taken longer to publish.
9. References
9.1. Normative References
[I-D.ietf-forces-protocol]
Dong, L., Doria, A., Gopal, R., HAAS, R., Salim, J.,
Khosravi, H., and W. Wang, "ForCES Protocol
Specification", draft-ietf-forces-protocol-22 (work in
progress), March 2009.
[RFC2404] Madson, C. and R. Glenn, "The Use of HMAC-SHA-1-96 within
ESP and AH", RFC 2404, November 1998.
[RFC2409] Harkins, D. and D. Carrel, "The Internet Key Exchange
(IKE)", RFC 2409, November 1998.
[RFC3554] Bellovin, S., Ioannidis, J., Keromytis, A., and R.
Stewart, "On the Use of Stream Control Transmission
Protocol (SCTP) with IPsec", RFC 3554, July 2003.
[RFC3602] Frankel, S., Glenn, R., and S. Kelly, "The AES-CBC Cipher
Algorithm and Its Use with IPsec", RFC 3602,
September 2003.
[RFC3758] Stewart, R., Ramalho, M., Xie, Q., Tuexen, M., and P.
Conrad, "Stream Control Transmission Protocol (SCTP)
Partial Reliability Extension", RFC 3758, May 2004.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, December 2005.
[RFC4960] Stewart, R., "Stream Control Transmission Protocol",
RFC 4960, September 2007.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
9.2. Informative References
[I-D.ietf-forces-model]
Halpern, J. and J. Salim, "ForCES Forwarding Element
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Model", draft-ietf-forces-model-16 (work in progress),
October 2008.
[I-D.ietf-tsvwg-sctpsocket]
Stewart, R., Poon, K., Tuexen, M., Yasevich, V., and P.
Lei, "Sockets API Extensions for Stream Control
Transmission Protocol (SCTP)",
draft-ietf-tsvwg-sctpsocket-20 (work in progress),
January 2010.
[RFC3654] Khosravi, H. and T. Anderson, "Requirements for Separation
of IP Control and Forwarding", RFC 3654, November 2003.
[RFC3746] Yang, L., Dantu, R., Anderson, T., and R. Gopal,
"Forwarding and Control Element Separation (ForCES)
Framework", RFC 3746, April 2004.
[RFC3768] Hinden, R., "Virtual Router Redundancy Protocol (VRRP)",
RFC 3768, April 2004.
Appendix A. Suggested SCTP TML Channel Work Implementation
As mentioned in Section 5, there are two levels of TML channel work
within an NE when a ForCES node (CE or FE) is connected to multiple
other ForCES nodes:
1. NE-level I/O work where a ForCES node (CE or FE) needs to choose
which of the peer nodes to process.
2. Node-level I/O work where a ForCES node, handles the three SCTP
TML channels separately for each single ForCES endpoint.
NE-level scheduling definition is left up to the implementation and
is considered out of scope for this document. Appendix A.4 discusses
briefly some constraints that an implementer needs to worry about.
This document and in particular Appendix A.1, Appendix A.2 and
Appendix A.3 discuss details of node-level I/O work.
A.1. SCTP TML Channel Initialization
As discussed in Section 5, it is recommended that the FE SHOULD do
socket connections to the CE in the order of incrementing priorities
i.e. LP socket first, followed by MP and ending with HP socket
connection. The CE, however, MUST NOT assume that there is ordering
of socket connections from any FE. Appendix B.1 has more details on
the expected initialization of SCTP channel work.
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A.2. Channel work scheduling
This section provides high level details of the scheduling view of
the SCTP TML core (Section 4.2.1). A practical scheduler
implementation takes care of many little details (such as timers,
work quanta, etc) not described in this document. It is left to the
implementer to take care of those details.
The CE(s) and FE(s) are coupled together in the principles of the
scheduling scheme described here to tie together node overload with
transport congestion. The design intent is to provide the highest
possible robust work throughput for the NE under any network or
processing congestion.
A.2.1. FE Channel work scheduling
The FE scheduling, in priority order, needs to I/O process:
1. The HP channel I/O in the following priority order:
1. Transmitting back to the CE any outstanding result of
executed work via the HP channel transmit path.
2. Taking new incoming work from the CE which creates ForCES
work to be executed by the FE.
2. ForCES events which result in transmission of unsolicited ForCES
packets to the CE via the MP channel.
3. Incoming Redirect work in the form of control packets that come
from the CE via LP channel. After redirect processing, these
packets get sent out on external (to the NE) interface.
4. Incoming Redirect work in the form of control packets that come
from other NEs via external (to the NE) interfaces. After some
processing, such packets are sent to the CE.
It is worth emphasizing at this point again that the SCTP TML
processes the channel work in strict priority. For example, as long
as there are messages to send to the CE on the HP channel, they will
be processed first until there are no more left before processing the
next priority work (which is to read new messages on the HP channel
incoming from the CE).
A.2.2. CE Channel work scheduling
The CE scheduling, in priority order, needs to deal with:
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1. The HP channel I/O in the following priority order:
1. Process incoming responses to requests of work it made to the
FE(s).
2. Transmitting any outstanding HP work it needs for the FE(s)
to complete.
2. Incoming ForCES events from the FE(s) via the MP channel.
3. Outgoing Redirect work in the form of control packets that get
sent from the CE via LP channel destined to external (to the NE)
interface on FE(s).
4. Incoming Redirect work in the form of control packets that come
from other NEs via external (to the NE) interfaces on the FE(s).
It is worth to repeat for emphasis again that the SCTP TML processes
the channel work in strict priority. For example, if there are
messages incoming from an FE on the HP channel, they will be
processed first until there are no more left before processing the
next priority work which is to transmit any outstanding HP channel
messages going to the FE.
A.3. SCTP TML Channel Termination
Appendix B.2 describes a controlled disassociation of the FE from the
NE.
It is also possible for connectivity to be lost between the FE and CE
on one or more sockets. In cases where SCTP multi-homing features
are used for path availability, the disconnection of a socket will
only occur if all paths are unreachable; otherwise, SCTP will ensure
reachability. In the situation of a total connectivity loss of even
one SCTP socket, it is recommended that the FE and CE SHOULD assume a
state equivalent to ForCES Association Teardown being issued and
follow the sequence described in Appendix B.2.
A CE could also disconnect sockets to an FE to indicate an "emergency
teardown". The "emergency teardown" may be necessary in cases when a
CE needs to disconnect an FE but knows that an FE is busy processing
a lot of outstanding commands (some of which the FE hasn't got around
to processing yet). By virtue of the CE closing the connections, the
FE will immediately be asynchronously notified and will not have to
process any outstanding commands from the CE.
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A.4. SCTP TML NE level channel scheduling
In handling NE-level I/O work, an implementation needs to worry about
being both fair and robust across peer ForCES nodes.
Fairness is desired so that each peer node makes progress across the
NE. For the sake of illustration consider two FEs connected to a CE;
whereas one FE has a few HP messages that need to be processed by the
CE, another may have infinite HP messages. The scheduling scheme may
decide to use a quota scheduling system to ensure that the second FE
does not hog the CE cycles.
Robustness is desired so that the NE does not succumb to a DoS attack
from hostile entities and always achieves a maximum stable workload
processing level. For the sake of illustration consider again two
FEs connected to a CE. Consider FE1 as having a large number of HP
and MP messages and FE2 having a large number of MP and LP messages.
The scheduling scheme needs to ensure that while FE1 always gets its
messages processed, at some point we allow FE2 messages to be
processed. A promotion and preemption based scheduling could be used
by the CE to resolve this issue.
Appendix B. Suggested Service Interface
This section outlines high level service interface between FEM/CEM
and TML, the PL and TML, and between local and remote TMLs. The
intent of this interface discussion is to provide general guidelines.
The implementer is expected to care of details and even follow a
different approach if needed.
The theory of operation for the PL-TML service is as follows:
1. The PL starts up and bootstraps the TML. The end result of a
successful TML bootstrap is that the CE TML and the FE TML
connect to each other at the transport level.
2. Transmission and reception of the PL messages commences after a
successful TML bootstrap. The PL uses send and receive PL-TML
interfaces to communicate to its peers. The TML is agnostic to
the nature of the messages being sent or received. The first
message exchanges that happen are to establish ForCES
association. Subsequent messages maybe either unsolicited events
from the FE PL, control message redirects from/to the CE to/from
FE, and configuration from the CE to the FE and their responses
flowing from the FE to the CE.
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3. The PL does a shutdown of the TML after terminating ForCES
association.
B.1. TML Boot-strapping
Figure 6 illustrates a flow for the TML bootstrapped by the PL.
When the PL starts up (possibly after some internal initialization),
it boots up the TML. The TML first interacts with the FEM/CEM and
acquires the necessary TML parameterization (Section 4.2.1.6). Next
the TML uses the information it retrieved from the FEM/CEM interface
to initialize itself.
The TML on the FE proceeds to connect the 3 channels to the CE. The
socket interface is used for each of the channels. The TML continues
to re-try the connections to the CE until all 3 channels are
connected. It is advisable that the number of connection retry
attempts and the time between each retry is also configurable via the
FEM. On failure to connect one or more channels, and after the
configured number of retry thresholds is exceeded, the TML will
return an appropriate failure indicator to the PL. On success (as
shown in Figure 6), a success indication is presented to the PL.
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FE PL FE TML FEM CEM CE TML CE PL
| | | | | |
| | | | | Bootup |
| | | | |<-------------------|
| Bootup | | | | |
|----------->| | |get CEM info| |
| |get FEM info | |<-----------| |
| |------------>| ~ ~ |
| ~ ~ |----------->| |
| |<------------| | |
| | |-initialize TML |
| | |-create the 3 chans.|
| | | to listen to FEs |
| | | |
| |-initialize TML |Bootup success |
| |-create the 3 chans. locally |------------------->|
| |-connect 3 chans. remotely | |
| |------------------------------>| |
| ~ ~ - FE TML connected ~
| ~ ~ - FE TML info init ~
| | channels connected | |
| |<------------------------------| |
| Bootup | | |
| succeeded | | |
|<-----------| | |
| | | |
Figure 6: SCTP TML Bootstrapping
On the CE things are slightly different. After initializing from the
CEM, the TML on the CE side proceeds to initialize the 3 channels to
listen to remote connections from the FEs. The success or failure
indication is passed on to the CE PL (in the same manner as was done
in the FE).
Post boot-up, the CE TML waits for connections from the FEs. Upon a
successful connection by an FE, the CE TML level keeps track of the
transport level details of the FE. Note, at this stage only
transport level connection has been established; ForCES level
association follows using send/receive PL-TML interfaces (refer to
Appendix B.3 and Figure 8).
B.2. TML Shutdown
Figure 7 shows an example of an FE shutting down the TML. It is
assumed at this point that the ForCES Association Teardown has been
issued by the CE. It should also be noted that different
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implementations may have different procedures for cleaning up state
etc.
When the FE PL issues a shutdown to its TML for a specific PL ID, the
TML releases all the channel connections to the CE. This is achieved
by closing the sockets used to communicate to the CE. This results
in the stack sending a SCTP shutdown which is received on the CE.
FE PL FE TML CE TML CE PL
| | | |
| Shutdown | | |
|----------->| | |
| |-disconnect 3 chans. | |
| |-SCTP level shutdown | |
| |------------------------>| |
| | | |
| | |TML detects shutdown|
| | |-FE TML info cleanup|
| | |-optionally tell PL |
| | |------------------->|
| | | |
| |- clean up any state of | |
| |-channels disconnected | |
| |<------------------------| |
| |-SCTP shutdown ACK | |
| | | |
| Shutdown | | |
| succeeded | | |
|<-----------| | |
| | | |
Figure 7: FE Shutting down
On the CE side, a TML disconnection would result in possible cleanup
of the FE state. Optionally, depending on the implementation, there
may be need to inform the PL about the TML disconnection. The CE
stack level SCTP sends an acknowledgement to the FE TML in response
to the earlier SCTP shutdown.
B.3. TML Sending and Receiving
The TML should be agnostic to the content of the PL messages, or
their operations. The PL should provide enough information to the
TML for it to assign an appropriate priority and loss behavior to the
message. Figure 8 shows an example of a message exchange originated
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at the FE and sent to the CE (such as a ForCES association message)
which illustrates all the necessary service interfaces for sending
and receiving.
When the FE PL sends a message to the TML, the TML is expected to
pick one of HP/MP/LP channels and send out the ForCES message.
FE PL FE TML CE TML CE PL
| | | |
|PL send | | |
|----------->| | |
| | | |
| | | |
| |-pick channel | |
| |-TML Send | |
| |------------->| |
| | | |
| | |-TML Receive on chan. |
| | |- mux to PL/PL recv |
| | |--------------------->|
| | | ~
| | | ~ PL Process
| | | ~
| | | PL send |
| | |<---------------------|
| | |-pick chan to send on |
| | |-TML send |
| |<-------------| |
| |-TML Receive | |
| |-mux to PL | |
| PL Recv | | |
|<---------- | | |
| | | |
Figure 8: Send and Recv Flow
When the CE TML receives the ForCES message on the channel it was
sent on, it demultiplexes the message to the CE PL.
The CE PL, after some processing (in this example dealing with the
FE's association), sends to the TML the response. And as in the case
of FE PL, the CE TML picks the channel to send on before sending.
The processing of the ForCES message upon arriving at the FE TML and
delivery to the FE PL is similar to the CE side equivalent as shown
above in Appendix B.3.
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Authors' Addresses
Jamal Hadi Salim
Mojatatu Networks
Ottawa, Ontario
Canada
Email: hadi@mojatatu.com
Kentaro Ogawa
NTT Corporation
3-9-11 Midori-cho
Musashino-shi, Tokyo 180-8585
Japan
Email: ogawa.kentaro@lab.ntt.co.jp
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