Routing IPv6 with IS-IS
RFC 5308
Document | Type |
RFC - Proposed Standard
(October 2008; No errata)
Updated by RFC 7775
Was draft-ietf-isis-ipv6 (isis WG)
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Author | Christian Hopps | ||
Last updated | 2015-10-14 | ||
Stream | IETF | ||
Formats | plain text html pdf htmlized bibtex | ||
Reviews | |||
Stream | WG state | (None) | |
Document shepherd | No shepherd assigned | ||
IESG | IESG state | RFC 5308 (Proposed Standard) | |
Consensus Boilerplate | Unknown | ||
Telechat date | |||
Responsible AD | Ross Callon | ||
Send notices to | (None) |
Network Working Group C. Hopps Request for Comments: 5308 Cisco Systems Category: Standards Track October 2008 Routing IPv6 with IS-IS Status of This Memo This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited. Abstract This document specifies a method for exchanging IPv6 routing information using the IS-IS routing protocol. The described method utilizes two new TLVs: a reachability TLV and an interface address TLV to distribute the necessary IPv6 information throughout a routing domain. Using this method, one can route IPv6 along with IPv4 and OSI using a single intra-domain routing protocol. 1. Overview IS-IS is an extendible intra-domain routing protocol. Each router in the routing domain issues an Link State Protocol Data Unit (LSP) that contains information pertaining to that router. The LSP contains typed variable-length data, often referred to as TLVs (type-length- values). We extend the protocol with two new TLVs to carry information required to perform IPv6 routing. In [RFC1195], a method is described to route both OSI and IPv4. We utilize this same method with some minor changes to allow for IPv6. To do so, we must define two new TLVs, namely "IPv6 Reachability" and "IPv6 Interface Address", and a new IPv6 protocol identifier. In our new TLVs, we utilize the extended metrics and up/down semantics of [RFC5305]. 1.1. 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 RFC 2119 [RFC2119]. Hopps Standards Track [Page 1] RFC 5308 Routing IPv6 with IS-IS October 2008 2. IPv6 Reachability TLV The "IPv6 Reachability" TLV is TLV type 236 (0xEC). [RFC1195] defines two Reachability TLVs, "IP Internal Reachability Information" and "IP External Reachability Information". We provide the equivalent IPv6 data with the "IPv6 Reachability" TLV and an "external" bit. The "IPv6 Reachability" TLV describes network reachability through the specification of a routing prefix, metric information, a bit to indicate if the prefix is being advertised down from a higher level, a bit to indicate if the prefix is being distributed from another routing protocol, and OPTIONALLY the existence of Sub-TLVs to allow for later extension. This data is represented by the following structure: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type = 236 | Length | Metric .. | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | .. Metric |U|X|S| Reserve | Prefix Len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Prefix ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Sub-TLV Len(*) | Sub-TLVs(*) ... * - if present U - up/down bit X - external original bit S - subtlv present bit The above IPv6 Reachability TLV MAY appear any number of times (including none) within an LSP. Link-local prefixes MUST NOT be advertised using this TLV. As is described in [RFC5305]: "The up/down bit SHALL be set to 0 when a prefix is first injected into IS-IS. If a prefix is advertised from a higher level to a lower level (e.g. level 2 to level 1), the bit SHALL be set to 1, indicating that the prefix has traveled down the hierarchy. Prefixes that have the up/down bit set to 1 may only be advertised down the hierarchy, i.e., to lower levels". If the prefix was distributed into IS-IS from another routing protocol, the external bit SHALL be set to 1. This information is useful when distributing prefixes from IS-IS to other protocols. Hopps Standards Track [Page 2] RFC 5308 Routing IPv6 with IS-IS October 2008 If the Sub-TLV bit is set to 0, then the octets of Sub-TLVs are not present. Otherwise, the bit is 1 and the octet following the prefix will contain the length of the Sub-TLV portion of the structure. The prefix is "packed" in the data structure. That is, only the required number of octets of prefix are present. This number can be computed from the prefix length octet as follows:Show full document text