Extensions to IS-IS for Layer-2 Systems
Two generic IS-IS building blocks that let a link state protocol carry Layer-2 port and MAC address information.
Banerjee, A. and D. Ward, "Extensions to IS-IS for Layer-2 Systems", RFC 6165, DOI 10.17487/RFC6165, April 2011, <https://www.rfc-editor.org/info/rfc6165>.
@misc{rfc6165,
series = {Request for Comments},
number = 6165,
howpublished = {RFC 6165},
publisher = {RFC Editor},
doi = {10.17487/RFC6165},
url = {https://www.rfc-editor.org/info/rfc6165},
author = {A. Banerjee and D. Ward},
title = {{Extensions to IS-IS for Layer-2 Systems}},
pagetotal = 7,
year = 2011,
month = apr,
} RFC text
Contents
Internet Engineering Task Force (IETF) A. Banerjee
Request for Comments: 6165 Cisco Systems
Category: Standards Track D. Ward
ISSN: 2070-1721 Juniper Networks
April 2011
Extensions to IS-IS for Layer-2 Systems
Abstract
This document specifies the Intermediate System to Intermediate
System (IS-IS) extensions necessary to support link state routing for
any protocols running directly over Layer-2. While supporting this
concept involves several pieces, this document only describes
extensions to IS-IS. Furthermore, the Type, Length, Value pairs
(TLVs) described in this document are generic Layer-2 additions, and
specific ones as needed are defined in the IS-IS technology-specific
extensions. We leave it to the systems using these IS-IS extensions
to explain how the information carried in IS-IS is used.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6165.
Copyright Notice
Copyright (c) 2011 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
(http://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. Overview ........................................................2
1.1. Terminology ................................................3
2. TLV Enhancements to IS-IS .......................................3
2.1. Multi-Topology-Aware Port Capability TLV ...................3
2.2. The MAC-Reachability TLV ...................................4
3. Acknowledgements ................................................5
4. Security Considerations .........................................5
5. IANA Considerations .............................................5
6. References ......................................................6
6.1. Normative References .......................................6
6.2. Informative References .....................................6
1. Overview
There are a number of systems (for example, [RBRIDGES], [802.1aq],
and [OTV]) that use Layer-2 addresses carried in a link state routing
protocol, specifically Intermediate System to Intermediate System
[IS-IS] [RFC1195], to provide true Layer-2 routing. In almost all
the technologies mentioned above, classical Layer-2 packets are
encapsulated with an outer header. The outer header format varies
across all these technologies. This outer header is used to route
the encapsulated packets to their destination.
Each Intermediate System (IS) advertises one or more IS-IS Link State
Protocol Data Units (PDUs) with routing information. Each Link State
PDU (LSP) is composed of a fixed header and a number of tuples, each
consisting of a Type, a Length, and a Value. Such tuples are
commonly known as TLVs. In this document, we specify a set of TLVs
to be added to [IS-IS] PDUs, to support these proposed systems. The
TLVs are generic Layer-2 additions, and specific ones, as needed, are
defined in the IS-IS technology-specific extensions. This document
does not propose any new forwarding mechanisms using this additional
information carried within IS-IS.
1.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
2. TLV Enhancements to IS-IS
This section specifies the enhancements for the TLVs that are needed
in common by Layer-2 technologies.
2.1. Multi-Topology-Aware Port Capability TLV
The Multi-Topology-aware Port Capability (MT-PORT-CAP) is IS-IS TLV
type 143 and has the following format:
+-+-+-+-+-+-+-+-+
| Type=MTPORTCAP| (1 byte)
+-+-+-+-+-+-+-+-+
| Length | (1 byte)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R|R|R|R| Topology Identifier | (2 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-TLVs (variable bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
o Type: TLV Type, set to MT-PORT-CAP TLV 143.
o Length: Total number of bytes contained in the value field,
including the length of the sub-TLVs carried in this TLV.
o R: Reserved 4 bits, MUST be sent as zero and ignored on receipt.
o Topology Identifier: MT ID is a 12-bit field containing the MT ID
of the topology being announced. This field when set to zero
implies that it is being used to carry base topology information.
o Sub-TLVs: The MT-PORT-CAP TLV value contains sub-TLVs formatted as
described in [RFC5305]. They are defined in the technology-
specific documents.
The MT-PORT-CAP TLV may occur multiple times and is carried within an
IS-IS Hello (IIH) PDU.
2.2. The MAC-Reachability TLV
The MAC-Reachability (MAC-RI) TLV is IS-IS TLV type 147 and has the
following format:
+-+-+-+-+-+-+-+-+
| Type= MAC-RI | (1 byte)
+-+-+-+-+-+-+-+-+
| Length | (1 byte)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Topology-id/Nickname | (2 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Confidence | (1 byte)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RESV | VLAN-ID | (2 bytes)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC (1) (6 bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ................. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MAC (N) (6 bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
o Type: TLV Type, set to 147 (MAC-RI).
o Length: Total number of bytes contained in the value field given
by 5 + 6*n bytes.
o Topology-id/Nickname : Depending on the technology in which it is
used, this carries the topology-id or nickname. When this field
is set to zero, this implies that the Media Access Control (MAC)
addresses are reachable across all topologies or across all
nicknames of the originating IS.
o Confidence: This carries an 8-bit quantity indicating the
confidence level in the MAC addresses being transported. Whether
this field is used, and its semantics if used, are further defined
by the specific protocol using Layer-2 IS-IS. If not used, it
MUST be set to zero on transmission and be ignored on receipt.
o RESV: (4 bits) MUST be sent as zero and ignored on receipt.
o VLAN-ID: This carries a 12-bit VLAN identifier that is valid for
all subsequent MAC addresses in this TLV, or the value zero if no
VLAN is specified.
o MAC(i): This is the 48-bit MAC address reachable from the IS that
is announcing this TLV.
The MAC-RI TLV is carried in a standard Link State PDU (LSP). This
TLV can be carried multiple times in an LSP and in multiple LSPs. It
MUST contain only unicast addresses. The manner in which these TLVs
are generated by the various Layer-2 routing technologies and the
manner in which they are consumed are detailed in the technology-
specific documents.
In most of the technologies, these MAC-RI TLVs will translate to
populating the hardware with these entries and with appropriate next-
hop information as derived from the advertising IS.
3. Acknowledgements
The authors would like to thank Peter Ashwood-Smith, Donald E.
Eastlake 3rd, Dino Farinacci, Don Fedyk, Les Ginsberg, Radia Perlman,
Mike Shand, and Russ White for their useful comments.
4. Security Considerations
This document adds no additional security risks to IS-IS, nor does it
provide any additional security for IS-IS.
5. IANA Considerations
This document specifies the definition of a set of new IS-IS TLVs --
the Port-Capability TLV (type 143) and the MAC-Reachability TLV
(type 147). They are listed in the IS-IS TLV codepoint registry.
IIH LSP SNP
MT-Port-Cap-TLV (143) X - -
MAC-RI TLV (147) - X -
6. References
6.1. Normative References
[IS-IS] ISO/IEC 10589:2002, Second Edition, "Intermediate System
to Intermediate System Intra-Domain Routing Information
Exchange Protocol for use in Conjunction with the Protocol
for Providing the Connectionless-mode Network Service
(ISO 8473)", 2002.
[RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
dual environments", RFC 1195, December 1990.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, October 2008.
6.2. Informative References
[802.1aq] "Standard for Local and Metropolitan Area Networks /
Virtual Bridged Local Area Networks / Amendment 8:
Shortest Path Bridging, Draft IEEE P802.1aq/D1.5", 2008.
[OTV] Grover, H., Rao, D., and D. Farinacci, "Overlay Transport
Virtualization", Work in Progress, October 2010.
[RBRIDGES]
Perlman, R., Eastlake 3rd, D., Dutt, D., Gai, S., and A.
Ghanwani, "RBridges: Base Protocol Specification", Work
in Progress, March 2010.
Authors' Addresses
Ayan Banerjee
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95138
USA
EMail: ayabaner@cisco.com
David Ward
Juniper Networks
1194 N. Mathilda Ave.
Sunnyvale, CA 94089-1206
USA
Phone: +1-408-745-2000
EMail: dward@juniper.net
AI ELI5
On this page
§1Why IS-IS Needs Layer-2 Extensions
Some systems, such as RBridges, 802.1aq (Shortest Path Bridging) and OTV, use Layer-2 addresses carried in a link state routing protocol to provide true Layer-2 routing. The protocol they use is Intermediate System to Intermediate System (IS-IS), as extended for IP in RFC 1195.
In almost all of these technologies, classical Layer-2 packets are encapsulated with an outer header, and that outer header is used to route the packet to its destination. The outer header format differs between the technologies.
Several different mail systems want to use the same postal map, even though their envelopes look different. This document gives them a shared way to write on the map.
§2What the RFC Covers and What It Leaves Out
Each Intermediate System (IS) advertises one or more Link State PDUs (LSPs). An LSP is a fixed header followed by a number of tuples, each made of a Type, a Length and a Value. These tuples are known as TLVs.
This document specifies a set of TLVs to add to IS-IS PDUs. They are generic Layer-2 additions. Specific ones, as needed, are defined in the IS-IS technology-specific extensions.
The RFC does not propose any new forwarding mechanism for the information it carries. It leaves it to the systems that use these extensions to explain how the information is used.
The document only says how to write the notes. It does not say what each mail system should do after reading them.
§2.1The Port Capability TLV
The Multi-Topology-aware Port Capability TLV (MT-PORT-CAP) is IS-IS TLV type 143. It has a 1-byte Type, a 1-byte Length, and then a 2-byte word made of 4 reserved bits and a 12-bit Topology Identifier. Sub-TLVs of variable size follow.
Lengthis the total number of bytes in the value field, including the sub-TLVs.- The four reserved bits (
R) MUST be sent as zero and ignored on receipt. - The Topology Identifier is the multi-topology ID of the topology being announced. Zero means the TLV carries base topology information.
- The sub-TLVs are formatted as described in RFC 5305 and are defined in the technology-specific documents.
The TLV may occur multiple times and is carried within an IS-IS Hello (IIH) PDU.
This is a small card a router hands to its neighbors saying what a port can do. The details on the card are filled in by each mail system's own rules.
| Field | Name | Size | Value | Description |
|---|---|---|---|---|
TYPE | Type | 1 byte | 143 | TLV type, set to 143. |
LENGTH | Length | 1 byte | Bytes in the value field, including sub-TLVs. | |
RESERVED | R | 4 bits | Reserved; sent as zero, ignored on receipt. | |
MT-ID | Topology Identifier | 12 bits | MT ID of the topology; zero means base topology. |
§2.2The MAC-Reachability TLV
The MAC-Reachability TLV (MAC-RI) is IS-IS TLV type 147. After the Type and Length it holds a 2-byte Topology-id/Nickname, a 1-byte Confidence, 4 reserved bits with a 12-bit VLAN-ID, and then one or more 6-byte MAC addresses. The Length is 5 + 6*n bytes for n addresses.
- Topology-id/Nickname carries a topology ID or a nickname, depending on the technology. Zero means the addresses are reachable across all topologies, or across all nicknames of the originating IS.
- Confidence is an 8-bit level of confidence in the addresses. Its meaning is left to the protocol using the TLV. If unused, it MUST be zero on transmission and ignored on receipt.
- VLAN-ID is a 12-bit VLAN identifier valid for all MAC addresses in the TLV, or zero if no VLAN is specified. The reserved bits MUST be zero and ignored on receipt.
- Each MAC entry is a 48-bit address reachable from the IS announcing the TLV.
The TLV is carried in a standard LSP, and can appear multiple times in an LSP and in multiple LSPs. It MUST contain only unicast addresses. In most technologies, these entries translate into populating hardware with the addresses and the next hop derived from the advertising IS.
This is an address-book page: a router lists the device addresses it can reach, so other routers know whom to ask when a message is for one of them.
| Field | Name | Size | Value | Description |
|---|---|---|---|---|
TYPE | Type | 1 byte | 147 | TLV type, set to 147. |
LENGTH | Length | 1 byte | 5 + 6*n bytes. | |
TOPO | Topology-id/Nickname | 2 bytes | Topology ID or nickname; zero means all. | |
CONFIDENCE | Confidence | 1 byte | Confidence level; zero if unused. | |
RESV | RESV | 4 bits | Reserved; sent as zero. | |
VLAN | VLAN-ID | 12 bits | VLAN for the MACs that follow, or zero. | |
MAC1 | MAC (1) | 4 bytes | First 48-bit unicast MAC address (continues in the next 16 bits). |
§3Security Considerations
The RFC is brief on security: it adds no additional security risks to IS-IS, and it does not provide any additional security for IS-IS either.
The new notes are no riskier than the old ones, and they are no better protected either.
§4IANA Registrations
The RFC defines two new IS-IS TLVs, listed in the IS-IS TLV codepoint registry: the Port-Capability TLV (type 143) and the MAC-Reachability TLV (type 147). The first appears in IIH PDUs. The second appears in LSPs. Neither is listed for sequence number PDUs (SNPs).
The two new kinds of note get official numbers in a public list, so nobody else reuses them.