Internet Engineering Task Force (IETF) J. Harrison

Internet Engineering Task Force (IETF) J. Harrison
Request for Comments: 6119 J. Berger
Category: Standards Track M. Bartlett
ISSN: 2070-1721 Metaswitch Networks
February 2011

IPv6 Traffic Engineering in IS-IS

Abstract

This document specifies a method for exchanging IPv6 traffic
engineering information using the IS-IS routing protocol. This
information enables routers in an IS-IS network to calculate traffic-
engineered routes using IPv6 addresses.

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/rfc6119.

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.

Harrison, et al. Standards Track [Page 1]

RFC 6119 IPv6 Traffic Engineering in IS-IS February 2011

This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
10, 2008. The person(s) controlling the copyright in some of this
material may not have granted the IETF Trust the right to allow
modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.

1. Overview

The IS-IS routing protocol is defined in [IS-IS]. Each router
generates a Link State PDU (LSP) that contains information describing
the router and the links from the router. The information in the LSP
is encoded in a variable length data structure consisting of a Type,
Length, and Value. Such a data structure is referred to as a TLV.

[TE] and [GMPLS] define a number of TLVs and sub-TLVs that allow
Traffic Engineering (TE) information to be disseminated by the IS-IS
protocol [IS-IS]. The addressing information passed in these TLVs is
IPv4 specific.

[IPv6] describes how the IS-IS protocol can be used to carry out
Shortest Path First (SPF) routing for IPv6. It does this by defining
IPv6-specific TLVs that are analogous to the TLVs used by IS-IS for
carrying IPv4 addressing information.

Multiprotocol Label Switching (MPLS) traffic engineering is very
successful, and, as the use of IPv6 grows, there is a need to be able
to support traffic engineering in IPv6 networks.

This document defines the TLVs that allow traffic engineering
information (including Generalized-MPLS (GMPLS) TE information) to be
carried in IPv6 IS-IS networks.

2. Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [KEYWORDS].

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RFC 6119 IPv6 Traffic Engineering in IS-IS February 2011

3. Summary of Operation

3.1. Identifying IS-IS Links Using IPv6 Addresses

Each IS-IS link has certain properties -- bandwidth, shared risk link
groups (SRLGs), switching capabilities, and so on. The IS-IS
extensions defined in [TE] and [GMPLS] describe how to associate
these traffic engineering parameters with IS-IS links. These TLVs
use IPv4 addresses to identify the link (or local/remote link
identifiers on unnumbered links).

When IPv6 is used, a numbered link may be identified by IPv4 and/or
IPv6 interface addresses. The type of identifier used does not
affect the properties of the link; it still has the same bandwidth,
SRLGs, and switching capabilities.

This document describes an approach for supporting IPv6 traffic
engineering by defining TLV extensions that allow TE links and nodes
to be identified by IPv6 addresses.

3.1.1. IPv6 Address Types

An IPv6 address can have global, unique-local, or link-local scope.

- A global IPv6 address is valid within the scope of the Internet.

- A unique-local IPv6 address is globally unique but is intended for
local communication.

- A link-local IPv6 address is valid only within the scope of a
single link and may only be referenced on that link.

Because the IPv6 traffic engineering TLVs present in LSPs are
propagated across networks, they MUST NOT use link-local addresses.

IS-IS does not need to differentiate between global and unique-local
addresses.

3.2. IP Addresses Used in Traffic Engineering TLVs

This section lists the IP addresses used in the TLVs defined in [TE]
and [GMPLS] and gives an overview of the required IPv6 equivalents.

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RFC 6119 IPv6 Traffic Engineering in IS-IS February 2011

3.2.1. TE Router ID TLV

The TE Router ID TLV contains a stable IPv4 address that is routable,
regardless of the state of each interface.

Similarly, for IPv6, it is useful to have a stable IPv6 address
identifying a TE node. The IPv6 TE Router ID TLV is defined in
Section 4.1.

3.2.2. IPv4 Interface Address Sub-TLV

This sub-TLV of the Extended IS Reachability TLV contains an IPv4
address for the local end of a link. The equivalent IPv6 Interface
Address sub-TLV is defined in Section 4.2.

3.2.3. IPv4 Neighbor Address Sub-TLV

This sub-TLV of the Extended IS Reachability TLV is used for point-
to-point links and contains an IPv4 address for the neighbor's end of
a link. The equivalent IPv6 Neighbor Address sub-TLV is defined in
Section 4.3.

A router constructs the IPv4 Neighbor Address sub-TLV using one of
the IPv4 addresses received in the IS-IS Hello (IIH) PDU from the
neighbor on the link.

The IPv6 Neighbor Address sub-TLV contains a globally unique IPv6
address for the interface from the peer (which can be either a global
or unique-local IPv6 address). The IPv6 Interface Address TLV
defined in [IPv6] only contains link-local addresses when used in the
IIH PDU. Hence, a neighbor's IP address from the IPv6 Interface
Address TLV cannot be used when constructing the IPv6 Neighbor
Address sub-TLV. Instead, we define an additional TLV, the IPv6
Global Interface Address TLV in Section 4.5. The IPv6 Global
Interface Address TLV is included in IIH PDUs to provide the globally
unique IPv6 address that a neighbor router needs in order to
construct the IPv6 Neighbor Address sub-TLV.

3.2.4. IPv4 SRLG TLV

The SRLG TLV (type 138) defined in [GMPLS] contains the set of SRLGs
associated with a link. The SRLG TLV identifies the link using
either local/remote IPv4 addresses or, for point-to-point unnumbered
links, link-local/remote identifiers. The SRLG TLV includes a flags
field to indicate which type of identifier is used.

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RFC 6119 IPv6 Traffic Engineering in IS-IS February 2011

When only IPv6 is used, IPv4 addresses and link-local/remote
identifiers are not available to identify the link, but IPv6
addresses can be used instead.

There is no backward-compatible way to modify the SRLG TLV (type 138)
to identify the link by IPv6 addresses; therefore, we need a new TLV.

The IPv6 SRLG TLV is defined in Section 4.4.

4. IPv6 TE TLVs

4.1. IPv6 TE Router ID TLV

The IPv6 TE Router ID TLV is TLV type 140.

The IPv6 TE Router ID TLV contains a 16-octet IPv6 address. A stable
global IPv6 address MUST be used, so that the router ID provides a
routable address, regardless of the state of a node's interfaces.

If a router does not implement traffic engineering, it MAY include or
omit the IPv6 TE Router ID TLV. If a router implements traffic
engineering for IPv6, it MUST include this TLV in its LSP. This TLV
MUST NOT be included more than once in an LSP.

An implementation receiving an IPv6 TE Router ID TLV MUST NOT
consider the router ID as a /128 reachable prefix in the standard SPF
calculation because this can lead to forwarding loops when
interacting with systems that do not support this TLV.

4.2. IPv6 Interface Address Sub-TLV

The IPv6 Interface Address sub-TLV of the Extended IS Reachability
TLV has sub-TLV type 12. It contains a 16-octet IPv6 address for the
interface described by the containing Extended IS Reachability TLV.
This sub-TLV can occur multiple times.

Implementations MUST NOT inject a /128 prefix for the interface
address into their routing or forwarding table because this can lead
to forwarding loops when interacting with systems that do not support
this sub-TLV.

If a router implements the basic TLV extensions described in [TE], it
MAY include or omit this sub-TLV. If a router implements IPv6
traffic engineering, it MUST include this sub-TLV (except on an
unnumbered point-to-point link, in which case the Link-Local
Interface Identifiers sub-TLV is used instead).

This sub-TLV MUST NOT contain an IPv6 link-local address.

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RFC 6119 IPv6 Traffic Engineering in IS-IS February 2011

4.3. IPv6 Neighbor Address sub-TLV

The IPv6 Neighbor Address sub-TLV of the Extended IS Reachability TLV
has sub-TLV type 13. It contains a 16-octet IPv6 address for a
neighboring router on the link described by the (main) TLV. This
sub-TLV can occur multiple times.

Implementations MUST NOT inject a /128 prefix for the interface
address into their routing or forwarding table because this can lead
to forwarding loops when interacting with systems that do not support
this sub-TLV.

If a router implements the basic TLV extensions described in [TE], it
MAY include or omit this sub-TLV. If a router implements IPv6
traffic engineering, it MUST include this sub-TLV for point-to-point
links (except on an unnumbered point-to-point link, in which case the
Link-Local Interface Identifiers sub-TLV is used instead).

This sub-TLV MUST NOT contain an IPv6 link-local address.

4.4. IPv6 SRLG TLV

The IPv6 SRLG TLV has type 139. The TLV carries the Shared Risk Link
Group information (see the "Shared Risk Link Group Information"
section of [GMPLS-ROUTING]).

It contains a data structure consisting of the following:

- 6 octets of System ID
- 1 octet of pseudonode number
- 1 octet flags
- 16 octets of IPv6 interface address
- (optional) 16 octets of IPv6 neighbor address
- (variable) list of SRLG values, where each element in the list has
4 octets

The following illustrates the encoding of the Value field of the IPv6
SRLG TLV.

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RFC 6119 IPv6 Traffic Engineering in IS-IS February 2011

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 ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| System ID (cont.) | Pseudonode num| Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 interface address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 interface address (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 interface address (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 interface address (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (optional) IPv6 neighbor address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 neighbor address (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 neighbor address (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 neighbor address (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Shared Risk Link Group Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ............ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Shared Risk Link Group Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The neighbor is identified by its System ID (6 octets), plus one
octet to indicate the pseudonode number if the neighbor is on a LAN
interface.

The 1-octet flags field is interpreted as follows.

Flags (1 octet)

0 1 2 3 4 5 6 7
+--+--+--+--+--+--+--+--+
| Reserved |NA|
+--+--+--+--+--+--+--+--+

NA - Neighbor Address included.

The flags field currently contains one flag to indicate whether the
IPv6 neighbor address is included (the NA bit is set to 1) or not
included (the NA bit is set to 0).

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RFC 6119 IPv6 Traffic Engineering in IS-IS February 2011

Other bits in the flags field are reserved for future use. Any bits
not understood by an implementation MUST be set to zero by the
sender. If a router receives an IPv6 SRLG TLV with non-zero values
for any bit that it does not understand, it MUST ignore the TLV (in
other words, it does not use the TLV locally but floods the TLV
unchanged to neighbors as normal).

Note that this rule for processing the flags octet allows for future
extensibility of the IPv6 SRLG TLV. In particular, it allows
alternative means of identifying the corresponding link to be added
in the future. An implementation that does not understand such an
extension will ignore the TLV rather than attempt to interpret the
TLV incorrectly.

The length of this TLV is 24 + 4 * (number of SRLG values) + 16 (if
the IPv6 neighbor address is included).

To prevent an SRLG TLV and an IPv6 SRLG TLV in the same logical LSP
from causing confusion of interpretation, the following rules are
applied.

- The IPv6 SRLG TLV MAY occur more than once within the IS-IS
logical LSP.

- There MUST NOT be more than one IPv6 SRLG TLV for a given link.

- The IPv6 SRLG TLV (type 139) MUST NOT be used to describe the
SRLGs for a given link if it is possible to use the SRLG TLV (type
138).

- If both an SRLG TLV and an IPv6 SRLG are received describing the
SRLGs for the same link, the receiver MUST apply the SRLG TLV and
ignore the IPv6 SRLG TLV.

In other words, if SRLGs are to be advertised for a link and if the
Extended IS Reachability TLV describing a link contains IPv4
interface/neighbor address sub-TLVs or the link-local identifiers
sub-TLV, then the SRLGs MUST be advertised in the SRLG TLV (type
138).

4.5. IPv6 Global Interface Address TLV

The IPv6 Global Interface Address TLV is TLV type 233. The TLV
structure is identical to that of the IPv6 Interface Address TLV
defined in [IPv6], but the semantics are different. In particular,
the TLV is included in IIH PDUs for those interfaces using IPv6 TE
extensions. The TLV contains global or unique-local IPv6 addresses
assigned to the interface that is sending the Hello.

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RFC 6119 IPv6 Traffic Engineering in IS-IS February 2011

The IPv6 Global Interface Address TLV is not used in LSPs.

5. Security Considerations

This document raises no new security issues for IS-IS; for general
security considerations for IS-IS, see [ISIS-AUTH].

6. IPv4/IPv6 Migration

The IS-IS extensions described in this document allow the routing of
GMPLS Label Switched Paths using IPv6 addressing through an IS-IS
network. There are no migration issues introduced by the addition of
this IPv6 TE routing information into an existing IPv4 GMPLS network.
Migration of Label Switched Paths from IPv4 to IPv6 is an issue for
GMPLS signaling and is outside the scope of this document.

7. IANA Considerations

This document defines the following new IS-IS TLV types that IANA has
reflected in the IS-IS TLV code-point registry:

Type Description IIH LSP SNP
---- ---------------------- --- --- ---
139 IPv6 SRLG TLV n y n
140 IPv6 TE Router ID n y n
233 IPv6 Global Interface y n n
Address TLV

This document also defines the following new sub-TLV types of top-
level TLV 22 that IANA has reflected in the Sub-TLVs for TLV 22, 141,
and 222 registry:

Type Description 22 141 222 Length
---- ----------- -- --- --- ------
12 IPv6 Interface Address y y y 16
13 IPv6 Neighbor Address y y y 16

8. Normative References

[IS-IS] ISO, "Intermediate System to Intermediate System intra-
domain routeing information exchange protocol for use in
conjunction with the protocol for providing the
connectionless-mode network service (ISO 8473)",
International Standard 10589: 2002, Second Edition, 2002.

[IPv6] Hopps, C., "Routing IPv6 with IS-IS", RFC 5308, October
2008.

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RFC 6119 IPv6 Traffic Engineering in IS-IS February 2011

[TE] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, October 2008.

[KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

[ISIS-AUTH] Li, T. and R. Atkinson, "IS-IS Cryptographic
Authentication", RFC 5304, October 2008.

[GMPLS] Kompella, K., Ed., and Y. Rekhter, Ed., "IS-IS Extensions
in Support of Generalized Multi-Protocol Label Switching
(GMPLS)", RFC 5307, October 2008.

[GMPLS-ROUTING]
Kompella, K., Ed., and Y. Rekhter, Ed., "Routing
Extensions in Support of Generalized Multi-Protocol Label
Switching (GMPLS)", RFC 4202, October 2005.

Authors' Addresses

Jon Harrison
Metaswitch Networks
100 Church Street
Enfield
EN2 6BQ
U.K.
Phone: +44 20 8366 1177
EMail: [email protected]

Jon Berger
Metaswitch Networks
100 Church Street
Enfield
EN2 6BQ
U.K.
Phone: +44 20 8366 1177
EMail: [email protected]

Mike Bartlett
Metaswitch Networks
100 Church Street
Enfield
EN2 6BQ
U.K.
Phone: +44 20 8366 1177
EMail: [email protected]

Harrison, et al. Standards Track [Page 10]