Extensions to IS-IS for Layer-2 Systems
Two IS-IS TLVs that let a link state protocol carry Layer-2 MAC addresses.
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
ISO Plain Language
On this page
§1Overview
There are a number of systems, for example RBridges, IEEE 802.1aq Shortest Path Bridging and Overlay Transport Virtualization, that use Layer-2 addresses carried in a link state routing protocol, specifically Intermediate System to Intermediate System, to provide true Layer-2 routing. In almost all of those technologies, classical Layer-2 packets are encapsulated with an outer header, and the format of that outer header varies from one technology to another. The outer header is what routes the encapsulated packets to their destination.
Each Intermediate System advertises one or more IS-IS Link State Protocol Data Units with routing information. Each Link State PDU is composed of a fixed header and a number of tuples, each consisting of a Type, a Length and a Value, and such tuples are commonly known as TLVs.
This document specifies a set of TLVs to be added to IS-IS PDUs to support these proposed systems. The TLVs are generic Layer-2 additions, and the specific ones that a given technology needs are defined in the IS-IS technology-specific extensions. This document does not propose any new forwarding mechanisms using the additional information carried within IS-IS.
When a frame crosses a Layer-2 network it is wrapped in an outer header, and that outer header is what carries it to the right place. The wrapping is different in every technology, but the routing information underneath can be shared, so this RFC adds generic fields to IS-IS that the individual technologies fill in as they need.
§2.1The Multi-Topology-Aware Port Capability TLV
The Multi-Topology-aware Port Capability, abbreviated MT-PORT-CAP, is IS-IS TLV type 143. Its format is a one-byte Type field set to 143, a one-byte Length field giving the total number of bytes in the value field including the length of the sub-TLVs it carries, then a two-byte field holding four reserved bits and a 12-bit Topology Identifier, then the sub-TLVs themselves in a variable number of bytes.
The four reserved bits must be sent as zero and ignored on receipt. The Topology Identifier is a 12-bit field containing the MT ID of the topology being announced, and when it is set to zero it implies that the TLV is being used to carry base topology information.
The sub-TLVs in the value field are formatted as described in RFC 5305, and 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 PDU.
This field goes in the Hello packets that neighbours exchange. It says which topology the port is on and then carries whatever details that particular Layer-2 technology wants to announce about it.
| Field | Name | Size | Value | Description |
|---|---|---|---|---|
TYPE | Type | 1 byte | 143 | TLV type, set to 143. |
LENGTH | Length | 1 byte | Total number of bytes in the value field, including the sub-TLVs it carries. | |
RESERVED | Reserved | 4 bits | Four reserved bits. Must be sent as zero and ignored on receipt. | |
TOPOLOGY-ID | Topology Identifier | 12 bits | 0 | The MT ID of the topology being announced. Zero means base topology information. |
SUB-TLVS | Sub-TLVs | 4 bytes | Sub-TLVs formatted as in RFC 5305, defined in the technology-specific documents. The number of bytes is variable. |
§2.2The MAC-Reachability TLV
The MAC-Reachability TLV, abbreviated MAC-RI, is IS-IS TLV type 147. Its format is a one-byte Type field set to 147, a one-byte Length field giving the total number of bytes in the value field, a two-byte Topology-id/Nickname field, a one-byte Confidence field, a two-byte field holding four reserved bits and a 12-bit VLAN-ID, and then the MAC addresses themselves, each six bytes long.
Depending on the technology in which it is used, the Topology-id/Nickname field carries the topology-id or the nickname. When it is set to zero this implies that the MAC addresses are reachable across all topologies, or across all nicknames, of the originating Intermediate System.
The Confidence field carries an 8-bit quantity indicating the confidence level in the MAC addresses being transported. Whether the field is used, and its semantics if it is, are defined further by the specific protocol using Layer-2 IS-IS. If it is not used, it must be set to zero on transmission and ignored on receipt.
The four reserved bits must be sent as zero and ignored on receipt. The VLAN-ID field carries a 12-bit VLAN identifier that is valid for all subsequent MAC addresses in the TLV, or the value zero if no VLAN is specified. Each MAC(i) entry is the 48-bit MAC address reachable from the Intermediate System that is announcing the TLV.
The MAC-RI TLV is carried in a standard Link State PDU. It 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 translate into populating the hardware with these entries, together with the appropriate next-hop information as derived from the advertising Intermediate System.
This field goes in the link state packets. It lists the hardware addresses that can be reached from the router sending it, along with the VLAN they sit in, and receivers normally load those entries into their forwarding hardware with a next hop taken from the same advertisement.
| Field | Name | Size | Value | Description |
|---|---|---|---|---|
TYPE | Type | 1 byte | 147 | TLV type, set to 147. |
LENGTH | Length | 1 byte | 17 | Total number of bytes in the value field, which is 5 plus 6 times the number of MAC addresses. |
TOPOLOGY-NICKNAME | Topology-id/Nickname | 2 bytes | 0 | The topology-id or the nickname, depending on the technology. Zero means reachable across all topologies or nicknames. |
CONFIDENCE | Confidence | 1 byte | 0 | An 8-bit confidence level in the MAC addresses. If unused it must be set to zero and ignored on receipt. |
RESV | RESV | 4 bits | Four reserved bits. Must be sent as zero and ignored on receipt. | |
VLAN-ID | VLAN-ID | 12 bits | 0 | A 12-bit VLAN identifier valid for all subsequent MAC addresses in this TLV, or zero if no VLAN is specified. |
MAC-1 | MAC (1) | 6 bytes | A 48-bit unicast MAC address reachable from the Intermediate System announcing this TLV. | |
MAC-N | MAC (N) | 6 bytes | Further MAC addresses follow, each 6 bytes long. |
§4Security Considerations
This document adds no additional security risks to IS-IS, nor does it provide any additional security for IS-IS.
Nothing new. The security of IS-IS as a whole is unchanged by these two fields, and they do not add any protection of their own.
§5IANA Considerations
The document specifies a set of new IS-IS TLVs, the Port-Capability TLV of type 143 and the MAC-Reachability TLV of type 147, and lists them in the IS-IS TLV codepoint registry.
The MT-Port-Cap-TLV of type 143 is carried in Hello PDUs and not in Link State PDUs or Sequence Numbers PDUs. The MAC-RI TLV of type 147 is carried in Link State PDUs and not in Hello PDUs or Sequence Numbers PDUs.
IANA keeps the list of IS-IS TLV numbers and records which kind of packet each one travels in. Two numbers are added here, one for Hello packets and one for link state packets.
- 143MT-Port-Cap-TLV — Carried in Hello PDUs. Announces the capabilities of a port for one topology.
- 147MAC-RI TLV — Carried in Link State PDUs. Lists the unicast MAC addresses reachable from the advertising router.