Network Working Group Christian Martin INTERNET DRAFT Verzion Global Networks, Inc. Brad Neal July 2001 Broadwing Communications A Policy Control Mechanism is IS-IS Using Administrative Tags 1. Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC 2026. 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. 2. Abstract This document describes an extension to the IS-IS protocol that adds to its operational capabilities, and that allows for easier management of and control over IP prefix distribution within an IS-IS domain. The IS-IS protocol is specified in [1], with extensions for supporting IPv4 specified in [2] and further enhancements for Traffic Engineering [4] in [3]. This document enhances the IS-IS protocol by augmenting the information that a Intermediate System (IS or router) can place in Link State Protocol Data Units (LSPs) as specified in [2]. Operators who must control the distribution of IP prefix information throughout a multilevel, large scale topology will find this useful. 3. Specification of Requirements Martin & Neal [Page 1] INTERNET DRAFT July 2001 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]. 4. Introduction As defined in [2] and extended in [3], the IS-IS protocol may be used to distribute IP prefix reachibility information throughout an IS-IS domain. The IP prefix information is encoded as TLV type 130 in [2], with additional information carried in TLV 135 as specified in [3]. In particular, the extended IP Reachibilty TLV (135) allows for a larger metric space, an up/down bit to indicate redistribution between different levels in the hierarchy, an IP prefix, and one or more sub- TLVs that can be used to carry specific information about the prefix. As of this writing no sub-TLVs have been defined. This draft, however, proposes a sub-TLV that may be used to carry administrative information about an IP prefix. 5. Sub-TLV Additions This draft proposes a new "Administrative Tag" sub-TLV to be added to TLV 135: a 32 bit unsigned integer that may be associated with an IP prefix. This tag may, among other things, be used to control redistribution among areas, routing protocols, or multiple instances of IS-IS running on the same router. The methods by which the feature is employed are beyond the scope of this document and are left to the implementer and/or operator. The encoding of the sub-TLV is discussed in the following subsection. 5.1. Administrative Tag Sub-TLV [TBA] This sub-TLV [TBA] shall be used to associate an integer value with an IP prefix such that it may be used in routing policy to control the distribution of routing information within an IS-IS domain. The Administrative Tag shall be encoded as a 4 octet unsigned integer. See the "IANA Considerations" section for additional information. 6. A compliant ISIS implementation... MUST be able to assign a policy tag to any IP prefix, for which it generates an extended IP reachability information TLV, MUST be able to assign more than one tag to a particular prefix, and Martin & Neal [Page 2] INTERNET DRAFT July 2001 SHOULD be able to rewrite or remove the policy-group of a received prefix according to its own policy. Unless stated otherwise, multiple occurrences of the tag are supported by multiple inclusions of the sub-TLV. 7. Operation An administrator associates a policy group identifier with some interesting property. When IS-IS advertises reachability for some IP prefix that has that property, it adds the policy identefier to the IP reachability information TLV for that prefix, and the tag "sticks" to the prefix as it is flooded throughout the routing domian. Consider the network in figure 1. We wish to "leak" L1 prefixes [5] with some property, A, from L2 to the L1 router R1. Without policy- groups, there is no way for R2 to know property A prefixes from property B prefixes. R2--------R3--------R4 L2 / \ - - - /- - - - - - - - - - - - - - L1 / \ R1 R5----1.1.1.0/24 (A) | | 1.1.2.0/24 (B) Figure 1 We associate policy-group 100 with property A, and have R5 attach that value to the IP extended reachability information TLV for prefix 1.1.1.0/24. R2 has a policy in place to "match prefixes with policy- group 100, and leak to L1." The previous example is rather simplistic; it seems that it would be just as easy for R2 simply to match the prefix 1.1.1.0/24. However, if there are a large number of routers that need to apply some policy according to property A and large number of "A" prefixes, this mechanism can be quite helpful. 8. Security Considerations This document raises no new security issues for IS-IS, as ; any annotations to IP prefixes should not pass outside the administrative control of the network operator of the IS-IS domain. Such an allowance would violate the spirit of Interior Gateway Protocols in general and IS-IS in particular. Martin & Neal [Page 3] INTERNET DRAFT July 2001 9. IANA Considerations The value of the Administrative Tag sub-TLV [TBA] must be allocated. 10. Acknowledgments The author would like to thank Henk Smit for clarifying the best place to describe this new information, Tony Li for useful comments on this draft, and Danny McPherson for some much needed formatting assistance. 11. References [1] "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. [2] Callon, R., RFC 1195, "Use of OSI IS-IS for routing in TCP/IP and dual environments", RFC 1195, December 1990. [3] Li, T., and Smit, H., "IS-IS extensions for Traffic Engineering", Internet Draft, "Work in Progress", September 2000. [4] Adwuche, D., Malcolm, J., Agogbua, M., O'Dell, M. and McManus, J., "Requirements for Traffic Engineering Over MPLS," RFC 2702, September 1999. [5] Li,T., Przygienda, T., Smit, H., "Domain-wide Prefix Distribution with Two-Level IS-IS" RFC 2966, October 2000 12. Authors' Address Christian Martin Verizon Global Networks, Inc. 1880 Campus Commons Dr Reston, VA 20191 USA Email: cmartin@gnilink.net Voice: 1 (703) 2954394 Fax: 1 (703) 2954279 Brad Neal Broadwing Communications 1835 Kramer Lane - Suite 100 Austin, TX 78758 USA Email: bneal@broadwing.com Voice: 1 (512) 7421310 Fax: 1 (512) 7421333 Martin & Neal [Page 4] INTERNET DRAFT July 2001