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(See Section 2.2 of https://www.ietf.org/id-info/checklist for how to handle the case when there are no actions for IANA.) == The 'Obsoletes: ' line in the draft header should list only the _numbers_ of the RFCs which will be obsoleted by this document (if approved); it should not include the word 'RFC' in the list. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year == The document doesn't use any RFC 2119 keywords, yet seems to have RFC 2119 boilerplate text. -- The document date (February 25, 2011) is 4102 days in the past. Is this intentional? Checking references for intended status: Informational ---------------------------------------------------------------------------- -- Obsolete informational reference (is this intentional?): RFC 1247 (Obsoleted by RFC 1583) -- Obsolete informational reference (is this intentional?): RFC 1583 (Obsoleted by RFC 2178) Summary: 2 errors (**), 0 flaws (~~), 3 warnings (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group A. Retana 3 Internet-Draft L. Nguyen 4 Obsoletes: RFC3137 R. White 5 (if approved) A. Zinin 6 Intended status: Informational Cisco Systems, Inc. 7 Expires: August 29, 2011 D. McPherson 8 Verisign, Inc. 9 February 25, 2011 11 OSPF Stub Router Advertisement 12 draft-retana-ospf-rfc3137bis-00 14 Abstract 16 This memo describes a backward-compatible technique that may be used 17 by OSPF (Open Shortest Path First) implementations to advertise 18 unavailability to forward transit traffic or to lower the preference 19 level for the paths through such a router. In some cases, it is 20 desirable not to route transit traffic via a specific OSPF router. 21 However, OSPF does not specify a standard way to accomplish this. 23 Status of this Memo 25 This Internet-Draft is submitted in full conformance with the 26 provisions of BCP 78 and BCP 79. 28 Internet-Drafts are working documents of the Internet Engineering 29 Task Force (IETF). Note that other groups may also distribute 30 working documents as Internet-Drafts. The list of current Internet- 31 Drafts is at http://datatracker.ietf.org/drafts/current/. 33 Internet-Drafts are draft documents valid for a maximum of six months 34 and may be updated, replaced, or obsoleted by other documents at any 35 time. It is inappropriate to use Internet-Drafts as reference 36 material or to cite them other than as "work in progress." 38 This Internet-Draft will expire on August 29, 2011. 40 Copyright Notice 42 Copyright (c) 2011 IETF Trust and the persons identified as the 43 document authors. All rights reserved. 45 This document is subject to BCP 78 and the IETF Trust's Legal 46 Provisions Relating to IETF Documents 47 (http://trustee.ietf.org/license-info) in effect on the date of 48 publication of this document. Please review these documents 49 carefully, as they describe your rights and restrictions with respect 50 to this document. Code Components extracted from this document must 51 include Simplified BSD License text as described in Section 4.e of 52 the Trust Legal Provisions and are provided without warranty as 53 described in the Simplified BSD License. 55 Table of Contents 57 1. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . 3 58 2. Requirements Language . . . . . . . . . . . . . . . . . . . . . 3 59 3. Proposed Solution . . . . . . . . . . . . . . . . . . . . . . . 3 60 4. Compatibility issues . . . . . . . . . . . . . . . . . . . . . 4 61 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 4 62 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 4 63 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5 64 7.1. Normative References . . . . . . . . . . . . . . . . . . . 5 65 7.2. Informative References . . . . . . . . . . . . . . . . . . 5 66 Appendix A. Changes from RFC 3137 . . . . . . . . . . . . . . . . 5 67 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 5 69 1. Motivation 71 In some situations, it may be advantageous to inform routers in a 72 network not to use a specific router as a transit point, but still 73 route to it. Possible situations include the following: 75 o The router is in a critical condition (for example, has very high 76 CPU load or does not have enough memory to store all LSAs or build 77 the routing table). 79 o Graceful introduction and removal of the router to/from the 80 network. 82 o Other (administrative or traffic engineering) reasons. 84 Note that the proposed solution does not remove the router from the 85 topology view of the network (as could be done by just flushing that 86 router's router-LSA), but prevents other routers from using it for 87 transit routing, while still routing packets to the router's own IP 88 addresses, i.e., the router is announced as a stub. 90 It must be emphasized that the proposed solution provides real 91 benefits in networks designed with at least some level of redundancy 92 so that traffic can be routed around the stub router. Otherwise, 93 traffic destined for the networks reachable through such a stub 94 router will be still routed through it. 96 2. Requirements Language 98 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 99 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 100 document are to be interpreted as described in RFC 2119 [RFC2119]. 102 3. Proposed Solution 104 The solution described in this document solves two challenges 105 associated with the outlined problem. In the description below, 106 router X is the router announcing itself as a stub. 108 1) Making other routers prefer routes around router X while 109 performing the Dijkstra calculation. 111 2) Allowing other routers to reach IP prefixes directly connected to 112 router X. 114 Note that it would be easy to address issue 1) alone by just flushing 115 router X's router-LSA from the domain. However, it does not solve 116 problem 2), since other routers will not be able to use links to 117 router X in Dijkstra (no back link), and because router X will not 118 have links to its neighbors. 120 To address both problems, router X announces its router-LSA to the 121 neighbors with the costs of all non-stub links (links of the types 122 other than 3) set to LSInfinity (16-bit value 0xFFFF, rather than 24- 123 bit value 0xFFFFFF used in summary and AS-external LSAs). 125 The solution above applies to both OSPFv2 [RFC2328] and OSPFv3 126 [RFC5340]. 128 4. Compatibility issues 130 Some inconsistency may be seen when the network is constructed of the 131 routers that perform intra-area Dijkstra calculation as specified in 132 RFC 1247 [RFC1247] (discarding link records in router-LSAs that have 133 LSInfinity cost value) and routers that perform it as specified in 134 RFC 1583 [RFC1583] and higher (do not treat links with LSInfinity 135 cost as unreachable). Note that this inconsistency will not lead to 136 routing loops, because if there are some alternate paths in the 137 network, both types of routers will agree on using them rather than 138 the path through the stub router. If the path through the stub 139 router is the only one, the routers of the first type will not use 140 the stub router for transit (which is the desired behavior), while 141 the routers of the second type will still use this path. 143 5. Security Considerations 145 The technique described in this document does not introduce any new 146 security issues into the OSPF protocol. 148 6. Acknowledgements 150 The authors of this document do not make any claims on the 151 originality of the ideas described. Among other people, we would 152 like to acknowledge Henk Smit for being part of one of the initial 153 discussions around this topic. 155 We would also like to thank Shishio Tsuchiya, Gunter Van de Velde and 156 Tomohiro Yamagata for reminding us of the need to document the OSPFv3 157 behavior. 159 7. References 161 7.1. Normative References 163 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 164 Requirement Levels", BCP 14, RFC 2119, March 1997. 166 7.2. Informative References 168 [RFC1247] Moy, J., "OSPF Version 2", RFC 1247, July 1991. 170 [RFC1583] Moy, J., "OSPF Version 2", RFC 1583, March 1994. 172 [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998. 174 [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF 175 for IPv6", RFC 5340, July 2008. 177 Appendix A. Changes from RFC 3137 179 o Edited in support for OSPFv3. 181 o Updated references and author information. 183 o Miscellaneous edits. 185 Authors' Addresses 187 Alvaro Retana 188 Cisco Systems, Inc. 189 7025 Kit Creek Rd. 190 Research Triangle Park, NC 27709 191 USA 193 Email: aretana@cisco.com 195 Liem Nguyen 196 Cisco Systems, Inc. 197 3750 Cisco Way 198 San Jose, CA 95134 199 USA 201 Phone: +1 408 527 0670 202 Email: lhnguyen@cisco.com 203 Russ White 204 Cisco Systems, Inc. 205 7025 Kit Creek Rd. 206 Research Triangle Park, NC 27709 207 USA 209 Email: russwh@cisco.com 211 Alex Zinin 212 Cisco Systems, Inc. 213 Capital Tower, 168 Robinson Rd. 214 Singapore, Singapore 068912 215 Singapore 217 Email: azinin@cisco.com 219 Danny McPherson 220 Verisign, Inc. 221 21345 Ridgetop Circle 222 Dulles, VA 20166 223 USA 225 Email: dmcpherson@verisign.com