Internet Draft Internet Engineering Task Force Christian E. Hopps INTERNET-DRAFT NextHop Technologies, Inc. Expires January 2001 10 July 2000 Routing IPv6 with IS-IS <draft-ietf-isis-ipv6-01.txt> Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Copyright Notice Copyright (C) The Internet Society (2000). All Rights Reserved. Expires January 2001 [Page 1] Draft Routing IPv6 with IS-IS July 2000 Abstract This draft specifies a method for exchanging IPv6 routing information using the IS-IS routing protocol [0]. The method utilizes the same mechanisms described in RFC 1195 [1]. This is accomplished by adding 2 new TLVs and defining their use. These new TLVs are patterned from the ones described in "IS-IS extensions for Traffic Engineering" [2]. Just as in RFC 1195 [1] with IPv4 and OSI, this method allows one to route both IPv4 and IPv6 using a single intra-domain routing protocol. 1. Terms 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. 2. Overview IS-IS is an extendible intra-domain routing protocol. Each router in the routing domain issues an 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 2 new TLVs to carry information required to perform IPv6 routing. In [1] 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 2 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 [2]. 3. IPv6 Reachability TLV The "IPv6 Reachability" TLV is TLV type 236 (0xEC). [1] defines 2 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. Expires January 2001 [Page 2] Draft Routing IPv6 with IS-IS July 2000 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: 4 octets of metric information 1 octet of control information 1 bit of up/down information 1 bit indicating external origination (e.g., from another routing protocol) 1 bit indicating the existence of sub-TLVs 5 reserved bits which must be zero and ignored 1 octet of prefix length 0-16 octets of prefix 0-249 optional octets of sub-TLVs, if present consisting of 1 octet of length of sub-TLVs 0-248 octets of sub-TLVs This structure may appear any number of times (including none) within the TLV. As is described in [2], "the up/down bit is set to 0 when a prefix is first injected into IS-IS. If a prefix is redistributed from a higher level to a lower level (e.g., level two to level one), the bit shall be set to 1 to indicate that the prefix has travelled down the hierarchy. If a prefix is redistributed from an area to another area at the same level then the up/down bit shall be set to 1." 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. If the sub-TLV bit is set to 0 then the optional 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: prefix octets = integer of ((prefix length + 7) / 8) Expires January 2001 [Page 3] Draft Routing IPv6 with IS-IS July 2000 Just as in [2], if a prefix is advertised with a metric larger than MAX_V6_PATH_METRIC (0xFE000000), this prefix must not be considered during the normal SPF computation. This will allow advertisement of a prefix for purposes other than building the normal IPv6 routing table. 4. IPv6 Interface Address TLV The "IPv6 Interface Address" TLV is TLV type 232 (0xE8). This TLV maps directly to [1]'s "IP Interface Address" TLV. We necessarily modify the contents to be 0-15 16 octet IPv6 interface addresses instead of 0-63 4 octet IPv4 interface address. We further restrict the semantics of this TLV depending on where it is advertised. For Hello PDUs the "Interfaces Address" TLV must contain only the link-local IPv6 addresses assigned to the interface which is sending the Hello. For LSPs the "Interfaces Address" TLVs must contain only the non-link-local IPv6 addresses assigned to the IS. 5. IPv6 NLPID The value of the IPv6 NLPID is 142 (0x8E). As with [1] and IPv4, if the IS supports IPv6 routing using IS-IS, it must advertise this in the "NLPID" TLV by adding the IPv6 NLPID. 6. Operation We utilize the same changes to [1] as made in [2] for the processing of prefix information. These changes are both related to the SPF calculation. Since the metric space has been extended we need to redefine the MAX_PATH_METRIC (1023) from the original specification in [1]. This new value MAX_V6_PATH_METRIC is the same as in [2] (0xFE000000). If during the SPF a path metric would exceed MAX_V6_PATH_METRIC it shall be considered to be MAX_V6_PATH_METRIC. The order of preference between paths for a given prefix must be modified to consider the up/down bit. The new order of preference is Expires January 2001 [Page 4] Draft Routing IPv6 with IS-IS July 2000 as follows (from best to worst). 1. Level 1 up prefix 2. Level 2 up prefix 3. Level 2 down prefix 4. Level 1 down prefix If multiple paths have the same best preference then selection occurs based on metric. Any remaining multiple paths should be considered for equal-cost multi-path routing if the router supports this, otherwise the router can select any one of the multiple paths. 7. Encapsulation of IS-IS PDUs There is no method currently defined for encapsulation of IS-IS PDUs in IPv6 packets. Based on further study, future versions of this draft may specify an optional method for encapsulating IS-IS PDUs in IPv6 packets. 8. Implementations An implementation of this draft has been completed in GateD. 9. Security Considerations This document raises no new security considerations. 10. References [0] "Intermediate System to Intermediate System Intra-Domain Routeing Exchange Protocol for use in Conjunction with the Protocol for Providing the Connectionless-mode Network Service (ISO 8473)", ISO 10589, 1992. [1] Callon, R., "Use of OSI IS-IS for Routing in TCP/IP and Dual Environments", RFC 1195, December 1990. [2] Smit, H., and T. Li, "IS-IS extensions for Traffic Engineering", Work in Progress, May 1999. Expires January 2001 [Page 5] Draft Routing IPv6 with IS-IS July 2000 11. Author's Address Christian E. Hopps NextHop Technologies, Inc. 4251 Plymouth Road, Building 1, Suite 2000. Ann Arbor, MI 48105 Phone: +1 734 936 0291 Email: chopps@djinesys.com 12. Full Copyright Statement Copyright (C) The Internet Society 2000. All Rights Reserved. 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