Layer 3 Discovery and Liveness
draft-ietf-lsvr-l3dl-06
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| Authors | Randy Bush , Rob Austein , Keyur Patel | ||
| Last updated | 2020-07-29 (Latest revision 2020-05-25) | ||
| Replaces | draft-ietf-lsvr-lsoe | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
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draft-ietf-lsvr-l3dl-06
Network Working Group R. Bush
Internet-Draft Arrcus & Internet Initiative Japan
Intended status: Standards Track R. Austein
Expires: January 30, 2021 K. Patel
Arrcus
July 29, 2020
Layer 3 Discovery and Liveness
draft-ietf-lsvr-l3dl-06
Abstract
In Massive Data Centers, BGP-SPF and similar routing protocols are
used to build topology and reachability databases. These protocols
need to discover IP Layer 3 attributes of links, such as neighbor IP
addressing, logical link IP encapsulation abilities, and link
liveness. This Layer 3 Discovery and Liveness protocol collects
these data, which may then be disseminated using BGP-SPF and similar
protocols.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 30, 2021.
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Copyright Notice
Copyright (c) 2020 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
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Background . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Top Level Overview . . . . . . . . . . . . . . . . . . . . . 6
5. Inter-Link Protocol Overview . . . . . . . . . . . . . . . . 7
5.1. L3DL Ladder Diagram . . . . . . . . . . . . . . . . . . . 7
6. Transport Layer . . . . . . . . . . . . . . . . . . . . . . . 9
7. The Checksum . . . . . . . . . . . . . . . . . . . . . . . . 11
8. TLV PDUs . . . . . . . . . . . . . . . . . . . . . . . . . . 13
9. Logical Link Endpoint Identifier . . . . . . . . . . . . . . 14
10. HELLO . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
11. OPEN . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
12. ACK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
12.1. Retransmission . . . . . . . . . . . . . . . . . . . . . 20
13. The Encapsulations . . . . . . . . . . . . . . . . . . . . . 20
13.1. The Encapsulation PDU Skeleton . . . . . . . . . . . . . 21
13.2. Encapsulaion Flags . . . . . . . . . . . . . . . . . . . 22
13.3. IPv4 Encapsulation . . . . . . . . . . . . . . . . . . . 22
13.4. IPv6 Encapsulation . . . . . . . . . . . . . . . . . . . 23
13.5. MPLS Label List . . . . . . . . . . . . . . . . . . . . 24
13.6. MPLS IPv4 Encapsulation . . . . . . . . . . . . . . . . 24
13.7. MPLS IPv6 Encapsulation . . . . . . . . . . . . . . . . 25
14. VENDOR - Vendor Extensions . . . . . . . . . . . . . . . . . 25
15. KEEPALIVE - Layer 2 Liveness . . . . . . . . . . . . . . . . 26
16. Layers 2.5 and 3 Liveness . . . . . . . . . . . . . . . . . . 27
17. The North/South Protocol . . . . . . . . . . . . . . . . . . 27
17.1. Use BGP-LS as Much as Possible . . . . . . . . . . . . . 28
17.2. Extensions to BGP-LS . . . . . . . . . . . . . . . . . . 28
18. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . 28
18.1. HELLO Discussion . . . . . . . . . . . . . . . . . . . . 28
18.2. HELLO versus KEEPALIVE . . . . . . . . . . . . . . . . . 29
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19. VLANs/SVIs/Sub-interfaces . . . . . . . . . . . . . . . . . . 29
20. Implementation Considerations . . . . . . . . . . . . . . . . 29
21. Security Considerations . . . . . . . . . . . . . . . . . . . 30
22. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30
22.1. PDU Types . . . . . . . . . . . . . . . . . . . . . . . 30
22.2. Signature Type . . . . . . . . . . . . . . . . . . . . . 31
22.3. Flag Bits . . . . . . . . . . . . . . . . . . . . . . . 31
22.4. Error Codes . . . . . . . . . . . . . . . . . . . . . . 31
23. IEEE Considerations . . . . . . . . . . . . . . . . . . . . . 32
24. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 32
25. References . . . . . . . . . . . . . . . . . . . . . . . . . 32
25.1. Normative References . . . . . . . . . . . . . . . . . . 32
25.2. Informative References . . . . . . . . . . . . . . . . . 34
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 35
1. Introduction
The Massive Data Center (MDC) environment presents unusual problems
of scale, e.g. O(10,000) forwarding devices, while its homogeneity
presents opportunities for simple approaches. Approaches such as
Jupiter Rising [JUPITER] use a central controller to deal with
scaling, while BGP-SPF [I-D.ietf-lsvr-bgp-spf] provides massive
scale-out without centralization using a tried and tested scalable
distributed control plane, offering a scalable routing solution in
Clos [Clos0][Clos1] and similar environments. But BGP-SPF and
similar higher level device-spanning protocols, e.g.
[I-D.malhotra-bess-evpn-lsoe], need logical link state and addressing
data from the network to build the routing topology. They also need
prompt but prudent reaction to (logical) link failure.
Layer 3 Discovery and Liveness (L3DL) provides brutally simple
mechanisms for devices to
o Discover each other's unique endpoint identification,
o Discover mutually supported layer 3 encapsulations, e.g. IP/MPLS,
o Discover Layer 3 IP and/or MPLS addressing of interfaces of the
encapsulations,
o Present these data, using a very restricted profile of a BGP-LS
[RFC7752] API, to BGP-SPF which computes the topology and builds
routing and forwarding tables,
o Enable Layer 3 link liveness such as BFD,
o Provide Layer 2 keep-alive messages for session continuity, and
finally
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o Provide for authenticity verification of protocol messages.
In this document, the use case for L3DL is for point to point links
in a datacenter Clos in order to exchange the data needed for BGP-SPF
[I-D.ietf-lsvr-bgp-spf] bootstrap and continuity. Once layer two
connectivity has been leveraged to get layer three addressability and
forwarding capabilities, normal layer three forwarding and routing
can take over.
L3DL might be found to be more widely applicable to a range of
routing and similar protocols which need layer three discovery and
characterisation.
2. Terminology
Even though it concentrates on the inter-device layer, this document
relies heavily on routing terminology. The following attempts to
clarify the use of some possibly confusing terms:
ASN: Autonomous System Number [RFC4271], a BGP identifier for
an originator of Layer 3 routes, particularly BGP
announcements.
BGP-LS: A mechanism by which link-state and TE information can be
collected from networks and shared with external
components using the BGP routing protocol. See [RFC7752].
BGP-SPF A hybrid protocol using BGP transport but a Dijkstra
Shortest Path First decision process. See
[I-D.ietf-lsvr-bgp-spf].
Clos: A hierarchic subset of a crossbar switch topology commonly
used in data centers.
Datagram: The L3DL content of a single Layer 2 frame, sans Ethernet
framing. A full L3DL PDU may be packaged in multiple
Datagrams.
Encapsulation: Address Family Indicator and Subsequent Address
Family Indicator (AFI/SAFI). I.e. classes of layer 2.5
and 3 addresses such as IPv4, IPv6, MPLS, etc.
Frame: A Layer 2 Ethernet packet.
Link or Logical Link: A logical connection between two logical ports
on two devices. E.g. two VLANs between the same two ports
are two links.
LLEI: Logical Link Endpoint Identifier, the unique identifier of
one end of a logical link, see Section 9.
MAC Address: 48-bit Layer 2 addresses are assumed since they are
used by all widely deployed Layer 2 network technologies
of interest, especially Ethernet. See [IEEE.802_2001].
MDC: Massive Data Center, commonly composed of thousands of Top
of Rack Switches (TORs).
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MTU: Maximum Transmission Unit, the size in octets of the
largest packet that can be sent on a medium, see [RFC1122]
1.3.3.
PDU: Protocol Data Unit, an L3DL application layer message. A
PDU's content may need to be broken into multiple
Datagrams to make it through MTU or other restrictions.
RouterID: An 32-bit identifier unique in the current routing domain,
see [RFC6286].
Session: An established, via OPEN PDUs, session between two L3DL
capable link end-points,
SPF: Shortest Path First, an algorithm for finding the shortest
paths between nodes in a graph; AKA Dijkstra's algorithm.
System Identifier: An eight octet ISO System Identifier a la
[RFC1629] System ID
TOR: Top Of Rack switch, aggregates the servers in a rack and
connects to aggregation layers of the Clos tree, AKA the
Clos spine.
ZTP: Zero Touch Provisioning gives devices initial addresses,
credentials, etc. on boot/restart.
3. Background
L3DL is primarily designed for a Clos type datacenter scale and
topology, but can accommodate richer topologies which contain
potential cycles.
While L3DL is designed for the MDC, there are no inherent reasons it
could not run on a WAN. The authentication and authorization needed
to run safely on a WAN need to be considered, and the appropriate
level of security options chosen.
L3DL assumes a new IEEE assigned EtherType (TBD).
The number of addresses of one Encapsulation type on an interface
link may be quite large given a TOR with tens of servers, each server
having a few hundred micro-services, resulting in an inordinate
number of addresses. And highly automated micro-service migration
can cause serious address prefix disaggregation, resulting in
interfaces with thousands of disaggregated prefixes.
Therefore the L3DL protocol is session oriented and uses incremental
announcement and withdrawal with session restart, a la BGP
([RFC4271]).
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4. Top Level Overview
o Devices discover each other on logical links
o Logical Link Endpoint Identifiers (LLEIs) are exchanged
o Layer 2 Liveness checks may be started
o Encapsulation data are exchanged and IP-Level Liveness checks
enabled
o A BGP-like upper layer protocol is assumed to use the identifiers
and encapsulation data to discover and build a topology database
+-------------------+ +-------------------+ +-------------------+
| Device | | Device | | Device |
| | | | | |
|+-----------------+| |+-----------------+| |+-----------------+|
|| || || || || ||
|| BGP-SPF <+---+> BGP-SPF <+---+> BGP-SPF ||
|| || || || || ||
|+--------^--------+| |+--------^--------+| |+--------^--------+|
| | | | | | | | |
| | | | | | | | |
|+--------+--------+| |+--------+--------+| |+--------+--------+|
|| Encapsulations || || Encapsulations || || Encapsulations ||
|| Addresses || || Addresses || || Addresses ||
|| L2 Liveness || || L2 Liveness || || L2 Liveness ||
|+--------^--------+| |+--------^--------+| |+--------^--------+|
| | | | | | | | |
| | | | | | | | |
|+--------v--------+| |+--------v--------+| |+--------v--------+|
|| || || || || ||
||Inter-Device PDUs<+---+>Inter-Device PDUs<+---+>Inter-Device PDUs||
|| || || || || ||
|+-----------------+| |+-----------------+| |+-----------------+|
+-------------------+ +-------------------+ +-------------------+
There are two protocols, the inter-device (left-right in the diagram)
per-link layer 3 discovery and the API to the upper level BGP-like
routing protocol (up-down in the above diagram):
o Inter-device PDUs are used to exchange device and logical link
identities and layer 2.5 (MPLS) and 3 identifiers (not payloads),
e.g. device IDs, port identities, VLAN IDs, Encapsulations, and IP
addresses.
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o A Link Layer to BGP API presents these data up the stack to a BGP
protocol or an other device-spanning upper layer protocol,
presenting them using the BGP-LS BGP-like data format.
The upper layer BGP family routing protocols cross all the devices,
though they are not part of these L3DL protocols.
To simplify this document, Layer 2 framing is not shown. L3DL is
about layer 3.
5. Inter-Link Protocol Overview
Two devices discover each other and their respective identities by
sending multicast HELLO PDUs (Section 10). To assure discovery of
new devices coming up on a multi-link topology, devices on such a
topology, and only on a multi-link topology, send periodic HELLOs
forever, see Section 18.1.
Once a new device is recognized, both devices attempt to negotiate
and establish a session by sending unicast OPEN PDUs (Section 11) to
the source MAC addresses (plus VIDs if VLANs) of the received HELLOs.
Once a session is established through the OPEN exchange, the
Encapsulations (Section 13) configured on an end point may be
announced and modified. Note that these are only the encapsulation
and addresses configured on the announcing interface; though a
device's loopback and overlay interface(s) may also be announced.
When two devices on a link have compatible Encapsulations and
addresses, i.e. the same AFI/SAFI and the same subnet, the link is
announced via the BGP-LS API.
5.1. L3DL Ladder Diagram
The HELLO, Section 10, is a priming message sent on all configured
logical links. It is a small L3DL PDU encapsulated in an Ethernet
multicast frame with the simple goal of discovering the identities of
logical link endpoint(s) reachable from a Logical Link Endpoint,
Section 9.
The HELLO and OPEN, Section 11, PDUs, which are used to discover and
exchange detailed Logical Link Endpoint Identifiers, LLEIs, and the
ACK/ERROR PDU, are mandatory; other PDUs are optional; though at
least one encapsulation SHOULD be agreed at some point.
The following is a ladder-style diagram of the L3DL protocol
exchanges:
| HELLO | Logical Link Peer discovery
|---------------------------->|
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| HELLO | Mandatory
|<----------------------------|
| |
| |
| OPEN | MACs, IDs, etc.
|---------------------------->|
| ACK |
|<----------------------------|
| |
| OPEN | Mandatory
|<----------------------------|
| ACK |
|---------------------------->|
| |
| |
| Interface IPv4 Addresses | Interface IPv4 Addresses
|---------------------------->| Optional
| ACK |
|<----------------------------|
| |
| Interface IPv4 Addresses |
|<----------------------------|
| ACK |
|---------------------------->|
| |
| |
| Interface IPv6 Addresses | Interface IPv6 Addresses
|---------------------------->| Optional
| ACK |
|<----------------------------|
| |
| Interface IPv6 Addresses |
|<----------------------------|
| ACK |
|---------------------------->|
| |
| |
| Interface MPLSv4 Labels | Interface MPLSv4 Labels
|---------------------------->| Optional
| ACK |
|<----------------------------|
| |
| Interface MPLSv4 Labels | Interface MPLSv4 Labels
|<----------------------------| Optional
| ACK |
|---------------------------->|
| |
| |
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| Interface MPLSv6 Labels | Interface MPLSv6 Labels
|---------------------------->| Optional
| ACK |
|<----------------------------|
| |
| Interface MPLSv6 Labels | Interface MPLSv6 Labels
|<----------------------------| Optional
| ACK |
|---------------------------->|
| |
| |
| L3DL KEEPALIVE | Layer 2 Liveness
|---------------------------->| Optional
| L3DL KEEPALIVE |
|<----------------------------|
6. Transport Layer
L3DL PDUs are carried by a simple transport layer which allows long
PDUs to occupy many Ethernet frames. The L3DL content of a single
Ethernet frame, exclusive of Ethernet framing data, is referred to as
a Datagram.
The L3DL Transport Layer encapsulates each Datagram using a common
transport header.
If a PDU does not fit in a single datagram, it is broken into
multiple Datagrams and reassembled by the receiver a la [RFC0791]
Section 2.3 Fragmentation.
This is not classic 'fragmentation', but rather decomposition at the
origin to allow PDU payloads larger than the frame allows. There are
no intermediate devices capable of further fragmentation or
reassembly.
A PDU might need a large number of frames to be sent. As fragments
are not ACK paced (as PDUs are), to avoid overwhelming bursts, the
sender should pace fragments of a large PDU.
L3DL is carrying relatively small amounts of data on relatively high
bandwidth links, and at a time when the link is not active with other
data as it does not yet have layer three connectivity. So congestion
is not considered a sufficiently significant risk to warrant
additional complexity.
Should a PDU need to be retransmitted, it MUST BE sent as the
identical Datagram set as the original transmission. The
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Transmission Sequence Number informs the receiver that it is the same
PDU.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version | Transmission Sequence Number |L| Dtgm Number ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Datagram Number (contd) | Datagram Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Payload... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The fields of the L3DL Transport Header are as follows:
Version: Eight-bit Version number of the protocol, currently 0.
Values other than 0 MUST BE treated as an error. The protocol
version needs to be in one and only one place, so it is in the
datagram as opposed to, for example, the PDU header.
Transmission Sequence Number: A 16-bit strictly increasing unsigned
integer identifying this PDU, possibly across retransmissions,
that wraps from 2^16-1 to 0. The initial value is arbitrary. See
[RFC1982] on DNS Serial Number Arithmetic for too much detail on
comparing and incrementing a wrapping sequence number.
L: A bit that set to one if this Datagram is the last Datagram of the
PDU. For a PDU which fits in only one Datagram, it is set to one.
Note that this is the inverse of the marking technique used by
[RFC0791].
Datagram Number: A monotonically increasing 23-bit value which
starts at zero for each PDU. This is used to reassemble frames
into PDUs a la [RFC0791] Section 2.3. Note that this limits an
L3DL PDU to 2^24 frames.
Datagram Length: Total number of octets in the Datagram including
all payloads and fields. Note that this limits a datagram to 2^16
octets; though Ethernet framing is likely to impose a smaller
limit.
Checksum: A 32 bit hash over the Datagram to detect bit flips, see
Section 7.
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If a Datagram fails checksum verification, the datagram is invalid
and should be silently discarded. The sender will retransmit the
PDU, and the receiver can assemble it.
Payload: The PDU being transported or a fragment thereof.
To avoid the need for a receiver to reassemble two PDUs at the same
time, a sender MUST NOT send a subsequent PDU when a PDU is already
in flight and not yet acknowledged; assuming it is an ACKed PDU Type.
7. The Checksum
There is a reason conservative folk use a checksum in UDP. And as
many operators stretch to jumbo frames (over 1,500 octets) longer
checksums are the prudent approach.
For the purpose of computing a checksum, the checksum field itself is
assumed to be zero.
The following code describes a suggested algorithm. This
specification avoids mandatory to implement, algorithm agility, etc.
What matters is that the same algorithm is used consistently in any
deployment.
Sum up 32-bit unsigned ints in a 64-bit long, then take the high-
order section, shift it right filling on the left with zeros, rotate,
add it in, repeat until the high order 32 bits are all zero.
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<CODE BEGINS>
#include <stddef.h>
#include <stdint.h>
/* The F table from Skipjack, and it would work for the S-Box. */
static const uint8_t sbox[256] = {
0xa3,0xd7,0x09,0x83,0xf8,0x48,0xf6,0xf4,0xb3,0x21,0x15,0x78,
0x99,0xb1,0xaf,0xf9,0xe7,0x2d,0x4d,0x8a,0xce,0x4c,0xca,0x2e,
0x52,0x95,0xd9,0x1e,0x4e,0x38,0x44,0x28,0x0a,0xdf,0x02,0xa0,
0x17,0xf1,0x60,0x68,0x12,0xb7,0x7a,0xc3,0xe9,0xfa,0x3d,0x53,
0x96,0x84,0x6b,0xba,0xf2,0x63,0x9a,0x19,0x7c,0xae,0xe5,0xf5,
0xf7,0x16,0x6a,0xa2,0x39,0xb6,0x7b,0x0f,0xc1,0x93,0x81,0x1b,
0xee,0xb4,0x1a,0xea,0xd0,0x91,0x2f,0xb8,0x55,0xb9,0xda,0x85,
0x3f,0x41,0xbf,0xe0,0x5a,0x58,0x80,0x5f,0x66,0x0b,0xd8,0x90,
0x35,0xd5,0xc0,0xa7,0x33,0x06,0x65,0x69,0x45,0x00,0x94,0x56,
0x6d,0x98,0x9b,0x76,0x97,0xfc,0xb2,0xc2,0xb0,0xfe,0xdb,0x20,
0xe1,0xeb,0xd6,0xe4,0xdd,0x47,0x4a,0x1d,0x42,0xed,0x9e,0x6e,
0x49,0x3c,0xcd,0x43,0x27,0xd2,0x07,0xd4,0xde,0xc7,0x67,0x18,
0x89,0xcb,0x30,0x1f,0x8d,0xc6,0x8f,0xaa,0xc8,0x74,0xdc,0xc9,
0x5d,0x5c,0x31,0xa4,0x70,0x88,0x61,0x2c,0x9f,0x0d,0x2b,0x87,
0x50,0x82,0x54,0x64,0x26,0x7d,0x03,0x40,0x34,0x4b,0x1c,0x73,
0xd1,0xc4,0xfd,0x3b,0xcc,0xfb,0x7f,0xab,0xe6,0x3e,0x5b,0xa5,
0xad,0x04,0x23,0x9c,0x14,0x51,0x22,0xf0,0x29,0x79,0x71,0x7e,
0xff,0x8c,0x0e,0xe2,0x0c,0xef,0xbc,0x72,0x75,0x6f,0x37,0xa1,
0xec,0xd3,0x8e,0x62,0x8b,0x86,0x10,0xe8,0x08,0x77,0x11,0xbe,
0x92,0x4f,0x24,0xc5,0x32,0x36,0x9d,0xcf,0xf3,0xa6,0xbb,0xac,
0x5e,0x6c,0xa9,0x13,0x57,0x25,0xb5,0xe3,0xbd,0xa8,0x3a,0x01,
0x05,0x59,0x2a,0x46
};
/* non-normative example C code, constant time even */
uint32_t sbox_checksum_32(const uint8_t *b, const size_t n)
{
uint32_t sum[4] = {0, 0, 0, 0};
uint64_t result = 0;
for (size_t i = 0; i < n; i++)
sum[i & 3] += sbox[*b++];
for (int i = 0; i < sizeof(sum)/sizeof(*sum); i++)
result = (result << 8) + sum[i];
result = (result >> 32) + (result & 0xFFFFFFFFU);
result = (result >> 32) + (result & 0xFFFFFFFFU);
return (uint32_t) result;
}
<CODE ENDS>
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8. TLV PDUs
The basic L3DL application layer PDU is a typical TLV (Type Length
Value) PDU. It includes a signature to provide optional integrity
and authentication. It may be broken into multiple Datagrams, see
Section 6.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PDU Type | Payload Length ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ | Payload ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sig Type | Signature Length | ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
~ Signature ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The fields of the basic L3DL header are as follows:
PDU Type: An integer differentiating PDU payload types. See
Section 22.1.
Payload Length: Total number of octets in the Payload field.
Payload: The application layer content of the L3DL PDU.
Sig Type: The type of the Signature, see Section 22.2. Type 0, a
null signature, is defined in this document.
Sig Type 0 indicates a null Signature. For a trivial PDU such as
KEEPALIVE, the underlying Datagram checksum may be sufficient for
integrity, though it lacks authenticity.
Other Sig Types may be defined in other documents, cf.
[I-D.ymbk-lsvr-l3dl-signing].
Signature Length: The length of the Signature, possibly including
padding, in octets. If Sig Type is 0, Signature Length MUST BE 0.
Signature: The result of running the signature algorithm specified
in Sig Type over all octets of the PDU except for the Signature
itself.
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9. Logical Link Endpoint Identifier
L3DL discovers neighbors on logical links and establishes sessions
between the two ends of all consenting discovered logical links. A
logical link is described by a pair of Logical Link Endpoint
Identifiers, LLEIs.
An LLEI is a variable length descriptor which could be an ASN, a
classic RouterID, a catenation of the two, an eight octet ISO System
Identifier [RFC1629], or any other identifier unique to a single
logical link endpoint in the topology.
An L3DL deployment will choose and define an LLEI which suits its
needs, simple or complex. Examples of two extremes follow:
A simplistic view of a link between two devices is two ports,
identified by unique MAC addresses, carrying a layer 3 protocol
conversation. In this case, the MAC addresses might suffice for the
LLEIs.
Unfortunately, things can get more complex. Multiple VLANs can run
between those two MAC addresses. In practice, many real devices use
the same MAC address on multiple ports and/or sub-interfaces.
Therefore, in the general circumstance, a fully described LLEI might
be as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ System Identifier +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ifIndex |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
System Identifier, a la [RFC1629], is an eight octet identifier
unique in the entire operational space. Routers and switches usually
have internal MAC Addresses which can be padded with high order zeros
and used if no System ID exists on the device. If no unique
identifier is burned into a device, the local L3DL configuration
SHOULD create and assign a unique one, likely by configuration.
ifIndex is the SNMP identifier of the (sub-)interface, see [RFC1213].
This uniquely identifies the port.
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For a layer 3 tagged sub-interface or a VLAN/SVI interface, Ifindex
is that of the logical sub-interface, so no further disambiguation is
needed.
L3DL PDUs learned over VLAN-ports may be interpreted by upper layer-3
routing protocols as being learned on the corresponding layer-3 SVI
interface for the VLAN.
LLEIs are big-endian.
10. HELLO
The HELLO PDU is unique in that it is encapsulated in a multicast
Ethernet frame. It solicits response(s) from other LLEI(s) on the
link. See Section 18.1 for why multicast is used. The destination
multicast MAC Addressees to be used MUST be one of the following, See
Clause 9.2.2 of [IEEE802-2014]:
01-80-C2-00-00-0E: Nearest Bridge = Propagation constrained to a
single physical link; stopped by all types of bridges (including
MPRs (media converters)). This SHOULD BE used when the link is
known to be a simple point to point link.
To Be Assigned: When a switch receives a frame with a multicast
destination MAC it does not recognize, it forwards to all ports.
This destination MAC is to be sent when the interface is known to
be connected to a switch. See Section 23. This SHOULD BE used
when the link may be a multi-point link.
All other L3DL PDUs are encapsulated in unicast frames, as the peer's
destination MAC address is known after the HELLO exchange.
When an interface is turned up on a device, it SHOULD issue a HELLO
if it is to participate in L3DL sessions.
If a constrained Nearest Bridge destination address has been
configured for a point-to-point interface, see above, then the HELLO
SHOULD NOT be repeated once a session has been created by an exchange
of OPENs.
If the configured destination address is one that is propagated by
switches, the HELLO SHOULD be repeated at a configured interval, with
a default of 60 seconds. This allows discovery by new devices which
come up on the layer-2 mesh. In this multi-link scenario, the
operator should be aware of the trade-off between timer tuning and
network noise and adjust the inter-HELLO timer accordingly.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PDU Type = 0 | Payload Length = 0 ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ | Sig Type = 0 | Signature Length = 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
If more than one device responds, one adjacency is formed for each
unique source LLEI response. L3DL treats each adjacency as a
separate logical link.
When a HELLO is received from a source MAC address (plus VID if VLAN)
with which there is no established L3DL session, the receiver SHOULD
respond by sending an OPEN PDU to the source MAC address (plus VID).
The two devices establish an L3DL session by exchanging OPEN PDUs.
To ameliorate possible load spikes during bootstrap or event
recovery, there SHOULD be a jittered delay between receipt of a HELLO
and issue of the OPEN. The default delay range SHOULD BE zero to
five seconds, and MUST be configurable.
If a HELLO is received from a MAC address with which there is an
established session, the HELLO should be dropped.
The Payload Length is zero as there is no payload.
HELLO PDUs can not be signed as keying material has yet to be
exchanged. Hence the signature MUST always be the null type.
11. OPEN
Each device has learned the other's MAC Address from the HELLO
exchange, see Section 10. Therefore the OPEN and all subsequent PDUs
MUST BE unicast, as opposed to the HELLO's multicast frame.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PDU Type = 1 | Payload Length ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ | Nonce ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ | LLEI Length | My LLEI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-~
~ | AttrCount | ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Attribute List ... | Auth Type | Key Length ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ | Key ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Serial Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sig Type | Signature Length | Signature ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Payload Length is the number of octets in all fields of the PDU
from the Nonce through the Serial Number, not including the three
final signature fields.
The Nonce enables detection of a duplicate OPEN PDU. It SHOULD be
either a random number or a high resolution timestamp. It is needed
to prevent session closure due to a repeated OPEN caused by a race or
a dropped or delayed ACK.
My LLEI is the sender's LLEI, see Section 9.
AttrCount is the number of attributes in the Attribute List.
Attributes are single octets the semantics of which are operator-
defined.
A node may have zero or more operator-defined attributes, e.g.:
spine, leaf, backbone, route reflector, arabica, ...
Attribute syntax and semantics are local to an operator or
datacenter; hence there is no global registry. Nodes exchange their
attributes only in the OPEN PDU.
Auth Type is the Signature algorithm suite, see Section 8.
Key Length is a 16-bit field denoting the length in octets of the Key
itself, not including the Auth Type or the Key Length. If the Auth
Type is zero, then the Key Length MUST also be zero, and there MUST
BE no Key data.
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The Key is specific to the operational environment. A failure to
authenticate is a failure to start the L3DL session, an ERROR PDU
MUST BE sent (Error Code 3), and HELLOs MUST be restarted.
Although delay and jitter in responding with an OPEN were specified
above, beware of load created by long strings of authentication
failures and retries. A configurable failure count limit (default 8)
SHOULD result in giving up on the connection attempt.
The Serial Number is that of the last received and processed PDU.
This allows a receiver sending an OPEN to tell the sender that the
receiver wants to resume a session and the sender only needs to send
data more recent than the Serial Number. If this OPEN is not trying
to restart a lost session, the Serial Number MUST BE set to zero.
The Signature fields are described in Section 8 and in an asymmetric
key environment serve as a proof of possession of the signing auth
data by the sender.
Once two logical link endpoints know each other, and have ACKed each
other's OPEN PDUs, Layer 2 KEEPALIVEs (see Section 15) MAY be started
to ensure Layer 2 liveness and keep the session semantics alive. The
timing and acceptable drop of KEEPALIVE PDUs are discussed in
Section 15.
If a sender of OPEN does not receive an ACK of the OPEN PDU, then
they MUST resend the same OPEN PDU, with the same Nonce. Resending
an unacknowledged OPEN PDU, like other ACKed PDUs, SHOULD use
exponential back-off, see [RFC1122].
If a properly authenticated OPEN arrives at L3DL speaker A with a new
Nonce from an LLEI, speaker B, with which A believes it already has
an L3DL session (OPENs have already been exchanged), and the Serial
Number in the OPEN PDU is non-zero, speaker A SHOULD establish a new
session by sending an OPEN with the Serial Number being the same as
that of A's last sent and ACKed PDU. Each party MUST resume sending
encapsulations etc. subsequent to the other party's Sequence Number.
And each MUST retain all previously discovered encapsulation and
other data.
If a properly authenticated OPEN arrives with a new Nonce from an
LLEI with which the receiving logical link endpoint believes it
already has an L3DL session (OPENs have already been exchanged), and
the Serial Number in the OPEN is zero, then the receiver MUST assume
that the sending LLEI or entire device has been reset. All
previously discovered encapsulation data MUST NOT be kept and MUST BE
withdrawn via the BGP-LS API and the recipient MUST respond with a
new OPEN.
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12. ACK
The ACK PDU acknowledges receipt of a PDU and reports any error
condition which might have been raised.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PDU Type = 3 | Payload Length = 5 ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ | ACKed PDU | EType | Error Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error Hint | Sig Type |Signature Leng.~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ | Signature ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The ACK acknowledges receipt of an OPEN, Encapsulation, VENDOR PDU,
etc.
The ACKed PDU is the PDU Type of the PDU being acknowledged, e.g.,
OPEN, one of the Encapsulations, etc.
If there was an error processing the received PDU, then the EType is
non-zero. If the EType is zero, Error Code and Error Hint MUST also
be zero.
A non-zero EType is the receiver's way of telling the PDU's sender
that the receiver had problems processing the PDU. The Error Code
and Error Hint will tell the sender more detail about the error.
The decimal value of EType gives a strong hint how the receiver
sending the ACK believes things should proceed:
0 - No Error, Error Code and Error Hint MUST be zero
1 - Warning, something not too serious happened, continue
2 - Session should not be continued, try to restart
3 - Restart is hopeless, call the operator
4-15 - Reserved
The Error Codes, noting protocol failures, are listed in
Section 22.4. Someone stuck in the 1990s might think the catenation
of EType and Error Code as an echo of 0x1zzz, 0x2zzz, etc. They
might be right; or not.
The Error Hint, an arbitrary 16 bits, is any additional data the
sender of the error PDU thinks will help the recipient or the
debugger with the particular error.
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The Signature fields are described in Section 8.
12.1. Retransmission
If a PDU sender expects an ACK, e.g. for an OPEN, an Encapsulation, a
VENDOR PDU, etc., and does not receive the ACK for a configurable
time (default one second), and the interface is live at layer 2, the
sender resends the PDU using exponential back-off, see [RFC1122].
This cycle MAY be repeated a configurable number of times (default
three) before it is considered a failure. The session MAY BE
considered closed in this case of this ACK failure.
If the link is broken at layer 2, retransmission MAY BE retried when
the link is restored.
13. The Encapsulations
Once the devices know each other's LLEIs, know each other's upper
layer (L2.5 and L3) identities, have means to ensure link state,
etc., the L3DL session is considered established, and the devices
SHOULD exchange L3 interface encapsulations, L3 addresses, and L2.5
labels.
The Encapsulation types the peers exchange may be IPv4
(Section 13.3), IPv6 (Section 13.4), MPLS IPv4 (Section 13.6), MPLS
IPv6 (Section 13.7), and/or possibly others not defined here.
The sender of an Encapsulation PDU MUST NOT assume that the peer is
capable of the same Encapsulation Type. An ACK (Section 12) merely
acknowledges receipt. Only if both peers have sent the same
Encapsulation Type is it safe for Layer 3 protocols to assume that
they are compatible for that type.
A receiver of an encapsulation might recognize an addressing
conflict, such as both ends of the link trying to use the same
address. In this case, the receiver SHOULD respond with an error
(Error Code 2) ACK. As there may be other usable addresses or
encapsulations, this error might log and continue, letting an upper
layer topology builder deal with what works.
Further, to consider a logical link of a type to formally be
established so that it may be pushed up to upper layer protocols, the
addressing for the type must be compatible, e.g. on the same IP
subnet.
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13.1. The Encapsulation PDU Skeleton
The header for all encapsulation PDUs is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PDU Type | Payload Length ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ | Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Serial Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Encapsulation List... | Sig Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Signature Length | Signature ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
An Encapsulation PDU describes zero or more addresses of the
encapsulation type.
The 24-bit Count is the number of Encapsulations in the Encapsulation
list.
The Serial Number is a monotonically increasing 32-bit value
representing the sender's state in time. It may be an integer, a
timestamp, etc. On session restart (new OPEN), a receiver MAY send
the last received Session Number to tell the sender to only send
newer data.
If a sender has multiple links on the same interface, separate state:
data, ACKs, etc. must be kept for each peer session.
Over time, multiple Encapsulation PDUs may be sent for an interface
as configuration changes.
If the length of an Encapsulation PDU exceeds the Datagram size limit
on media, the PDU is broken into multiple Datagrams. See Section 8.
The Signature fields are described in Section 8.
The Receiver MUST acknowledge the Encapsulation PDU with a Type=3,
ACK PDU (Section 12) with the Encapsulation Type being that of the
encapsulation being announced, see Section 12.
If the Sender does not receive an ACK in a configurable interval
(default one second), and the interface is live at layer 2, they
SHOULD retransmit. After a user configurable number of failures
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(default three), the L3DL session should be considered dead and the
OPEN process SHOULD be restarted.
If the link is broken at layer 2, retransmission MAY BE retried if
data have not changed in the interim.
13.2. Encapsulaion Flags
The Encapsulation Flags are a sequence of bit fields as follows:
0 1 2 3 4 ... 7
+------------+------------+------------+------------+------------+
| Ann/With | Primary | Under/Over | Loopback | Reserved ..|
+------------+------------+------------+------------+------------+
Each encapsulation in an Encapsulation PDU of Type T may announce new
and/or withdraw old encapsulations of Type T. It indicates this with
the Ann/With Encapsulation Flag, Announce == 1, Withdraw == 0.
Each Encapsulation interface address in an Encapsulation PDU is
either a new encapsulation be announced (Ann/With == 1) (yes, a la
BGP) or requests one be withdrawn (Ann/With == 0). Adding an
encapsulation which already exists SHOULD raise an Announce/Withdraw
Error (see Section 22.4); the EType SHOULD be 2, suggesting a session
restart (see Section 12 so all encapsulations will be resent.
If an LLEI has multiple addresses for an encapsulation type, one and
only one address MAY be marked as primary (Primary Flag == 1) for
that Encapsulation Type.
An Encapsulation interface address in an Encapsulation PDU MAY be
marked as a loopback, in which case the Loopback bit is set.
Loopback addresses are generally not seen directly on an external
interface. One or more loopback addresses MAY be exposed by
configuration on one or more L3DL speaking external interfaces, e.g.
for iBGP peering. They SHOULD be marked as such, Loopback Flag == 1.
Each Encapsulation interface address in an Encapsulation PDU is that
of the direct 'underlay interface (Under/Over == 1), or an 'overlay'
address (Under/Over == 0), likely that of a VM or container guest
bridged or configured on to the interface already having an underlay
address.
13.3. IPv4 Encapsulation
The IPv4 Encapsulation describes a device's ability to exchange IPv4
packets on one or more subnets. It does so by stating the
interface's addresses and the corresponding prefix lengths.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PDU Type = 4 | Payload Length ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ | Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Serial Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Encaps Flags | IPv4 Address ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ | PrefixLen | more ... | Sig Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Signature Length | Signature ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The 24-bit Count is the sum of the number of IPv4 Encapsulations
being announced and/or withdrawn.
13.4. IPv6 Encapsulation
The IPv6 Encapsulation describes a logical link's ability to exchange
IPv6 packets on one or more subnets. It does so by stating the
interface's addresses and the corresponding prefix lengths.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PDU Type = 5 | Payload Length ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ | Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Serial Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Encaps Flags | |
+-+-+-+-+-+-+-+-+ +
| |
+ +
| |
+ +
| IPv6 Address |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | PrefixLen | more ... | Sig Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Signature Length | Signature ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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The 24-bit Count is the sum of the number of IPv6 Encapsulations
being announced and/or withdrawn.
13.5. MPLS Label List
As an MPLS enabled interface may have a label stack, see [RFC3032], a
variable length list of labels is needed. These are the labels the
sender will accept for the prefix to which the list is attached.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label Count | Label | Exp |S|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label | Exp |S| more ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
A Label Count of zero is an implicit withdraw of all labels for that
prefix on that interface.
13.6. MPLS IPv4 Encapsulation
The MPLS IPv4 Encapsulation describes a logical link's ability to
exchange labeled IPv4 packets on one or more subnets. It does so by
stating the interface's addresses the corresponding prefix lengths,
and the corresponding labels which will be accepted for each address.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PDU Type = 6 | Payload Length ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ | Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Serial Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Encaps Flags | MPLS Label List ... | ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ IPv4 Address | PrefixLen |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| more ... | Sig Type | Signature Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Signature |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The 24-bit Count is the sum of the number of MPLSv4 Encapsulation
being announced and/or withdrawn.
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13.7. MPLS IPv6 Encapsulation
The MPLS IPv6 Encapsulation describes a logical link's ability to
exchange labeled IPv6 packets on one or more subnets. It does so by
stating the interface's addresses, the corresponding prefix lengths,
and the corresponding labels which will be accepted for each address.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PDU Type = 7 | Payload Length ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ | Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Serial Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Encaps Flags | MPLS Label List ... | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| |
+ +
| |
+ +
| IPv6 Address |
+ +-+-+-+-+-+-+-+-+
| | Prefix Len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| more ... | Sig Type | Signature Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Signature ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The 24-bit Count is the sum of the number of MPLSv6 Encapsulations
being announced and/or withdrawn.
14. VENDOR - Vendor Extensions
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PDU Type = 255| Payload Length ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ | Serial Number ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ | Enterprise Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ent Type | Enterprise Data ... ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ | Sig Type | Signature Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Signature ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Vendors or enterprises may define TLVs beyond the scope of L3DL
standards. This is done using a Private Enterprise Number [IANA-PEN]
followed by Enterprise Data in a format defined for that Enterprise
Number and Ent Type.
Ent Type allows a VENDOR PDU to be sub-typed in the event that the
vendor/enterprise needs multiple PDU types.
As with Encapsulation PDUs, a receiver of a VENDOR PDU MUST respond
with an ACK or an ERROR PDU. Similarly, a VENDOR PDU MUST only be
sent over an open session.
15. KEEPALIVE - Layer 2 Liveness
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PDU Type = 2 | Payload Length = 0 ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ | Sig Type = 0 | Signature Length = 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
L3DL devices SHOULD beacon frequent Layer 2 KEEPALIVE PDUs to ensure
session continuity. The inter-KEEPALIVE interval is configurable,
with a default of ten seconds. A receiver may choose to ignore
KEEPALIVE PDUs.
An operational deployment MUST BE configured whether to use
KEEPALIVEs or not, either globally, or as finely as to per-link
granularity. Disagreement MAY result in repeated session failure and
reestablishment.
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KEEPALIVEs SHOULD be beaconed at a configured frequency. One per
second is the default. Layer 3 liveness, such as BFD, may be more
(or less) aggressive.
When a sender transmits a PDU which is not a KEEPALIVE, the sender
SHOULD reset the KEEPALIVE timer. I.e. sending any PDU acts as a
keepalive. Once the last fragment has been sent, the KEEPALIVE timer
SHOULD BE restarted. Do not wait for the ACK.
If a KEEPALIVE or other PDUs have not been received from a peer with
which a receiver has an open session for a configurable time (default
30 seconds), the link SHOULD BE presumed down. The devices MAY keep
configuration state and restore it without retransmission if no data
have changed. Otherwise, a new session SHOULD BE established and new
Encapsulation PDUs exchanged.
16. Layers 2.5 and 3 Liveness
Layer 2 liveness may be continuously tested by KEEPALIVE PDUs, see
Section 15. As layer 2.5 or layer 3 connectivity could still break,
liveness above layer 2 MAY be frequently tested using BFD ([RFC5880])
or a similar technique.
This protocol assumes that one or more Encapsulation addresses may be
used to ping, run BFD, or whatever the operator configures.
17. The North/South Protocol
Thus far, a one-hop point-to-point logical link discovery protocol
has been defined.
The devices know their unique LLEIs and know the unique peer LLEIs
and Encapsulations on each logical link interface.
Full topology discovery is not appropriate at the L3DL layer, so
Dijkstra a la IS-IS etc. is assumed to be done by higher level
protocols such as BGP-SPF.
Therefore the LLEIs, link Encapsulations, and state changes are
pushed North via a small subset of the BGP-LS API. The upper layer
routing protocol(s), e.g. BGP-SPF, learn and maintain the topology,
run Dijkstra, and build the routing database(s).
For example, if a neighbor's IPv4 Encapsulation address changes, the
devices seeing the change push that change Northbound.
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17.1. Use BGP-LS as Much as Possible
BGP-LS [RFC7752] defines BGP-like Datagrams describing logical link
state (links, nodes, link prefixes, and many other things), and a new
BGP path attribute providing Northbound transport, all of which can
be ingested by upper layer protocols such as BGP-SPF; see Section 4
of [I-D.ietf-lsvr-bgp-spf].
For IPv4 links, TLVs 259 and 260 are used. For IPv6 links, TLVs 261
and 262. If there are multiple addresses on a link, multiple TLV
pairs are pushed North, having the same ID pairs.
17.2. Extensions to BGP-LS
The Northbound protocol needs a few minor extensions to BGP-LS.
Luckily, others have needed the same extensions.
Similarly to BGP-SPF, the BGP protocol is used in the Protocol-ID
field specified in table 1 of
[I-D.ietf-idr-bgpls-segment-routing-epe]. The local and remote node
descriptors for all NLRI are the IDs described in Section 11. This
is equivalent to an adjacency SID or a node SID if the address is a
loopback address.
Label Sub-TLVs from [I-D.ietf-idr-bgp-ls-segment-routing-ext]
Section 2.1.1, are used to associate one or more MPLS Labels with a
link.
18. Discussion
This section explores some trade-offs taken and some considerations.
18.1. HELLO Discussion
A device with multiple Layer 2 interfaces, traditionally called a
switch, may be used to forward frames and therefore packets from
multiple devices to one logical interface (LLEI), I, on an L3DL
speaking device. Interface I could discover a peer J across the
switch. Later, a prospective peer K could come up across the switch.
If I was not still sending and listening for HELLOs, the potential
peering with K could not be discovered. Therefore, on multi-link
interfaces, L3DL MUST continue to send HELLOs as long as they are
turned up.
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18.2. HELLO versus KEEPALIVE
Both HELLO and KEEPALIVE are periodic. KEEPALIVE might be eliminated
in favor of keeping only HELLOs. But KEEPALIVEs are unicast, and
thus less noisy on the network, especially if HELLO is configured to
transit layer-2-only switches, see Section 18.1.
19. VLANs/SVIs/Sub-interfaces
One can think of the protocol as an instance (i.e. state machine)
which runs on each logical link of a device.
As the upper routing layer must view VLAN topologies as separate
graphs, L3DL treats VLAN ports as separate links.
L3DL PDUs learned over VLAN-ports may be interpreted by upper layer-3
routing protocols as being learned on the corresponding layer-3 SVI
interface for the VLAN.
As Sub-Interfaces each have their own LLIEs, they act as separate
interfaces, forming their own links.
20. Implementation Considerations
An implementation SHOULD provide the ability to configure each
logical interface as L3DL speaking or not.
An implementation SHOULD provide the ability to configure whether
HELLOs on an L3DL enabled interface send Nearest Bridge or the MAC
which is propagated by switches from that interface; see Section 10.
An implementation SHOULD provide the ability to distribute one or
more loopback addresses or interfaces into L3DL on an external L3DL
speaking interface.
An implementation SHOULD provide the ability to distribute one or
more overlay and/or underlay addresses or interfaces into L3DL on an
external L3DL speaking interface.
An implementation SHOULD provide the ability to configure one of the
addresses of an encapsulation as primary on an L3DL speaking
interface. If there is only one address for a particular
encapsulation, the implementation MAY mark it as primary by default.
An implementation MAY allow optional configuration which updates the
local forwarding table with overlay and underlay data both learned
from L3DL peers and configured locally.
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21. Security Considerations
The protocol as is MUST NOT be used outside a datacenter or similarly
closed environment without authentication and authorization
mechanisms such as [I-D.ymbk-lsvr-l3dl-signing].
Many MDC operators have a strange belief that physical walls and
firewalls provide sufficient security. This is not credible. All
MDC protocols need to be examined for exposure and attack surface.
In the case of L3DL, Authentication and Integrity as provided in
[I-D.ymbk-lsvr-l3dl-signing] is strongly recommended.
It is generally unwise to assume that on the wire Layer 2 is secure.
Strange/unauthorized devices may plug into a port. Mis-wiring is
very common in datacenter installations. A poisoned laptop might be
plugged into a device's port, form malicious sessions, etc. to
divert, intercept, or drop traffic.
Similarly, malicious nodes/devices could mis-announce addressing.
If OPENs are not being authenticated, an attacker could forge an OPEN
for an existing session and cause the session to be reset.
For these reasons, the OPEN PDU's authentication data exchange SHOULD
be used.
If the KEEPALIVE PDU is not signed (as suggested in Section 8) to
save computation, then a MITM could fake a session being alive.
22. IANA Considerations
22.1. PDU Types
This document requests the IANA create a registry for L3DL PDU Type,
which may range from 0 to 255. The name of the registry should be
L3DL-PDU-Type. The policy for adding to the registry is RFC Required
per [RFC5226], either standards track or experimental. The initial
entries should be the following:
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PDU
Code PDU Name
---- -------------------
0 HELLO
1 OPEN
2 KEEPALIVE
3 ACK
4 IPv4 Announcement
5 IPv6 Announcement
6 MPLS IPv4 Announcement
7 MPLS IPv6 Announcement
8-254 Reserved
255 VENDOR
22.2. Signature Type
This document requests the IANA create a registry for L3DL Signature
Type, AKA Sig Type, which may range from 0 to 255. The name of the
registry should be L3DL-Signature-Type. The policy for adding to the
registry is RFC Required per [RFC5226], either standards track or
experimental. The initial entries should be the following:
Number Name
------ -------------------
0 Null
1-255 Reserved
22.3. Flag Bits
This document requests the IANA create a registry for L3DL PL Flag
Bits, which may range from 0 to 7. The name of the registry should
be L3DL-PL-Flag-Bits. The policy for adding to the registry is RFC
Required per [RFC5226], either standards track or experimental. The
initial entries should be the following:
Bit Bit Name
---- -------------------
0 Announce/Withdraw (ann == 0)
1 Primary
2 Underlay/Overlay (under == 0)
3 Loopback
4-7 Reserved
22.4. Error Codes
This document requests the IANA create a registry for L3DL Error
Codes, a 16 bit integer. The name of the registry should be L3DL-
Error-Codes. The policy for adding to the registry is RFC Required
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per [RFC5226], either standards track or experimental. The initial
entries should be the following:
Error
Code Error Name
---- -------------------
0 No Error
1 Checksum Error
2 Logical Link Addressing Conflict
3 Authorization Failure
4 Announce/Withdraw Error
23. IEEE Considerations
This document requires a new EtherType.
This document requires a new multicast MAC address that will be
broadcast through a switch.
24. Acknowledgments
The authors thank Cristel Pelsser for multiple reviews, Harsha Kovuru
for comments during implementation, Jeff Haas for review and
comments, Joerg Ott for an early but deep transport review, Joe
Clarke for a useful review, John Scudder for deeply serious review
and comments, Larry Kreeger for a lot of layer 2 clue, Martijn
Schmidt for his contribution, Nalinaksh Pai for transport
discussions, Neeraj Malhotra for review, Paul Congdon for Ethernet
hints, Russ Housley for checksum discussion and sBox, and Steve
Bellovin for checksum advice.
25. References
25.1. Normative References
[I-D.ietf-idr-bgp-ls-segment-routing-ext]
Previdi, S., Talaulikar, K., Filsfils, C., Gredler, H.,
and M. Chen, "BGP Link-State extensions for Segment
Routing", draft-ietf-idr-bgp-ls-segment-routing-ext-16
(work in progress), June 2019.
[I-D.ietf-idr-bgpls-segment-routing-epe]
Previdi, S., Talaulikar, K., Filsfils, C., Patel, K., Ray,
S., and J. Dong, "BGP-LS extensions for Segment Routing
BGP Egress Peer Engineering", draft-ietf-idr-bgpls-
segment-routing-epe-19 (work in progress), May 2019.
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[I-D.ietf-lsvr-bgp-spf]
Patel, K., Lindem, A., Zandi, S., and W. Henderickx,
"Shortest Path Routing Extensions for BGP Protocol",
draft-ietf-lsvr-bgp-spf-10 (work in progress), July 2020.
[I-D.ymbk-lsvr-l3dl-signing]
Bush, R. and R. Austein, "Layer 3 Discovery and Liveness
Signing", draft-ymbk-lsvr-l3dl-signing-01 (work in
progress), May 2020.
[IANA-PEN]
"IANA Private Enterprise Numbers",
<https://www.iana.org/assignments/enterprise-numbers/
enterprise-numbers>.
[IEEE.802_2001]
IEEE, "IEEE Standard for Local and Metropolitan Area
Networks: Overview and Architecture", IEEE 802-2001,
DOI 10.1109/ieeestd.2002.93395, July 2002,
<http://ieeexplore.ieee.org/servlet/opac?punumber=7732>.
[IEEE802-2014]
Institute of Electrical and Electronics Engineers, "Local
and Metropolitan Area Networks: Overview and
Architecture", IEEE Std 802-2014, 2014.
[RFC1213] McCloghrie, K. and M. Rose, "Management Information Base
for Network Management of TCP/IP-based internets: MIB-II",
STD 17, RFC 1213, DOI 10.17487/RFC1213, March 1991,
<https://www.rfc-editor.org/info/rfc1213>.
[RFC1629] Colella, R., Callon, R., Gardner, E., and Y. Rekhter,
"Guidelines for OSI NSAP Allocation in the Internet",
RFC 1629, DOI 10.17487/RFC1629, May 1994,
<https://www.rfc-editor.org/info/rfc1629>.
[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>.
[RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001,
<https://www.rfc-editor.org/info/rfc3032>.
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[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006,
<https://www.rfc-editor.org/info/rfc4271>.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<https://www.rfc-editor.org/info/rfc5226>.
[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
<https://www.rfc-editor.org/info/rfc5880>.
[RFC6286] Chen, E. and J. Yuan, "Autonomous-System-Wide Unique BGP
Identifier for BGP-4", RFC 6286, DOI 10.17487/RFC6286,
June 2011, <https://www.rfc-editor.org/info/rfc6286>.
[RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
S. Ray, "North-Bound Distribution of Link-State and
Traffic Engineering (TE) Information Using BGP", RFC 7752,
DOI 10.17487/RFC7752, March 2016,
<https://www.rfc-editor.org/info/rfc7752>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
25.2. Informative References
[Clos0] Clos, C., "A study of non-blocking switching networks
[PAYWALLED]", Bell System Technical Journal 32 (2), pp
406-424, March 1953.
[Clos1] "Clos Network",
<https://en.wikipedia.org/wiki/Clos_network/>.
[I-D.malhotra-bess-evpn-lsoe]
Malhotra, N., Patel, K., and J. Rabadan, "LSoE-based PE-CE
Control Plane for EVPN", draft-malhotra-bess-evpn-lsoe-00
(work in progress), March 2019.
[JUPITER] Singh, A., Ong, J., Agarwal, A., Anderson, G., Armistead,
A., Bannon, R., Boving, S., Desai, G., Felderman, B.,
Germano, P., Kanagala, A., Liu, H., Provost, J., Simmons,
J., Tanda, E., Wanderer, J., HAP.lzle, U., Stuart, S., and
A. Vahdat, "Jupiter rising", Communications of the
ACM Vol. 59, pp. 88-97, DOI 10.1145/2975159, August 2016.
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[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
DOI 10.17487/RFC0791, September 1981,
<https://www.rfc-editor.org/info/rfc791>.
[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>.
[RFC1982] Elz, R. and R. Bush, "Serial Number Arithmetic", RFC 1982,
DOI 10.17487/RFC1982, August 1996,
<https://www.rfc-editor.org/info/rfc1982>.
Authors' Addresses
Randy Bush
Arrcus & Internet Initiative Japan
5147 Crystal Springs
Bainbridge Island, WA 98110
US
Email: randy@psg.com
Rob Austein
Arrcus, Inc
Email: sra@hactrn.net
Keyur Patel
Arrcus
2077 Gateway Place, Suite #400
San Jose, CA 95119
US
Email: keyur@arrcus.com
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