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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Obsolete normative reference: RFC 4020 (Obsoleted by RFC 7120) ** Obsolete normative reference: RFC 5226 (Obsoleted by RFC 8126) Summary: 2 errors (**), 0 flaws (~~), 1 warning (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Inter-Domain Routing A. Retana 3 Internet-Draft Hewlett-Packard Co. 4 Intended status: Standards Track R. White 5 Expires: May 24, 2012 Cisco Systems, Inc. 6 November 21, 2011 8 BGP Custom Decision Process 9 draft-ietf-idr-custom-decision-00 11 Abstract 13 The BGP specification defines a Decision Process for installation of 14 routes into the Loc-RIB. This process takes into account an 15 extensive series of path attributes, which can be manipulated to 16 indicate preference for specific paths. It is cumbersome (if at all 17 possible) for the end user to define policies that will select, after 18 partial comparison, a path based on subjective local (domain and/or 19 node) criteria. 21 This document defines a new Extended Community, called the Cost 22 Community, which may be used in tie breaking during the best path 23 selection process. The end result is a local custom decision 24 process. 26 Status of this Memo 28 This Internet-Draft is submitted in full conformance with the 29 provisions of BCP 78 and BCP 79. 31 Internet-Drafts are working documents of the Internet Engineering 32 Task Force (IETF). Note that other groups may also distribute 33 working documents as Internet-Drafts. The list of current Internet- 34 Drafts is at http://datatracker.ietf.org/drafts/current/. 36 Internet-Drafts are draft documents valid for a maximum of six months 37 and may be updated, replaced, or obsoleted by other documents at any 38 time. It is inappropriate to use Internet-Drafts as reference 39 material or to cite them other than as "work in progress." 41 This Internet-Draft will expire on May 24, 2012. 43 Copyright Notice 45 Copyright (c) 2011 IETF Trust and the persons identified as the 46 document authors. All rights reserved. 48 This document is subject to BCP 78 and the IETF Trust's Legal 49 Provisions Relating to IETF Documents 50 (http://trustee.ietf.org/license-info) in effect on the date of 51 publication of this document. Please review these documents 52 carefully, as they describe your rights and restrictions with respect 53 to this document. Code Components extracted from this document must 54 include Simplified BSD License text as described in Section 4.e of 55 the Trust Legal Provisions and are provided without warranty as 56 described in the Simplified BSD License. 58 Table of Contents 60 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 61 2. Requirements Language . . . . . . . . . . . . . . . . . . . . . 3 62 3. The BGP Cost Community . . . . . . . . . . . . . . . . . . . . 3 63 4. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 64 5. Deployment Considerations . . . . . . . . . . . . . . . . . . . 5 65 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 66 7. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 67 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6 68 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7 69 9.1. Normative References . . . . . . . . . . . . . . . . . . . 7 70 9.2. Informative References . . . . . . . . . . . . . . . . . . 7 71 Appendix A. Cost Community Point of Insertion Registry . . . . . . 7 72 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8 74 1. Introduction 76 There are a number of metrics available within the BGP decision 77 process [RFC4271] which can be used to determine the exit point for 78 traffic, but there is no metric, or combination of metrics, which can 79 be used to break a tie among generally equal paths. 81 o LOCAL_PREF: The LOCAL_PREF is an absolute tie breaker near the 82 beginning of the decision process. There is no way to configure 83 the LOCAL_PREF such that the MED, IGP metric, and other metrics 84 are considered before breaking a tie. 86 o MED: The MULTI_EXIT_DISC is an indicator of which local entrance 87 point an AS would like a peering AS to use; MED isn't suitable to 88 break the tie between two equal cost paths learned from two peer 89 ASes. MED is also compared before the IGP metric; there is no way 90 to set the MED so a path with a higher IGP metric is preferred 91 over a path with a lower IGP metric. 93 o IGP Metric: It is possible, using the IGP metric, to influence 94 individual paths with otherwise equal cost metrics, but only by 95 changing the next hop towards each path, and configuring the IGP 96 costs of reaching each next hop. This method is cumbersome, and 97 prone to confusion and error. 99 The BGP specification defines a Decision Process for installation of 100 routes into the Loc-RIB. This process takes into account an 101 extensive series of path attributes, which can be manipulated to 102 indicate preference for specific paths. It is cumbersome (if at all 103 possible) for the end user to define policies that will select, after 104 partial comparison, a path based on subjective local (domain and/or 105 node) criteria. 107 This document defines a new Extended Community, called the Cost 108 Community, which may be used in tie breaking during the best path 109 selection process. The end result is a custom decision process. 111 2. Requirements Language 113 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 114 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 115 document are to be interpreted as described in [RFC2119]. 117 3. The BGP Cost Community 119 The BGP Cost Community is an Opaque Extended Community [RFC4360] 120 defined as follows: 122 Type Field: 123 The value of the high-order octet of this Opaque Extended 124 Community is 0x03 or 0x43. The value of the low-order octet of 125 the extended type field for this community is 0x01. 127 Value Field: 128 The Value field contains three distinct sub-fields, described 129 below: 131 +------------------------------+ 132 | Point of Insertion (1 octet) | 133 +------------------------------+ 134 | Community-ID (1 octet) | 135 +------------------------------+ 136 | Cost (4 octets) | 137 +------------------------------+ 139 The Point of Insertion sub-field contains the value of the path 140 attribute *after* which this community MUST be considered during 141 the best path selection process. 143 The BGP decision process includes some steps that do not 144 correspond to any path attribute; the following values are 145 defined: 147 128 ABSOLUTE_VALUE - Indicates that the Cost Community MUST be 148 considered as the first step in determining the Degree of 149 Preference of a path. 151 129 IGP_COST - Indicates that the Cost Community MUST be 152 considered after the interior (IGP) distance to the next-hop 153 has been compared. 155 130 EXTERNAL_INTERNAL - Indicates that the Cost Community MUST 156 be considered after the paths advertised by BGP speakers in 157 a neighboring autonomous system (if any) have been selected. 159 131 BGP_ID - Indicates that the Cost Community MUST be 160 considered after the BGP Identifier (or ORIGINATOR_ID 161 [RFC4456]) has been compared. 163 The Community-ID sub-field contains an identifier to distinguish 164 between multiple instances of the Cost Community. 166 The Cost sub-field contains a value assigned by the network 167 administrator and that is significant to the local autonomous 168 system. The lower cost MUST be preferred. The default value is 169 0x7FFFFFFF (half the maximum value). 171 4. Operation 173 The network administrator may use the Cost Community to assign a 174 value to a path originated or learned from a peer in any part of the 175 local domain. The Point of Insertion may also be specified using the 176 values assigned by IANA (Section 6) or this document. 178 If a BGP speaker receives a path that contains the Cost Community, it 179 SHOULD consider its value at the Point of Insertion specified, when 180 calculating the best path [RFC4271]. 182 If the Point of Insertion is not valid for the local best path 183 selection implementation, then the Cost Community SHOULD be silently 184 ignored. Paths that do not contain the Cost Community (for a valid, 185 particular Point of Insertion) MUST be considered to have the default 186 value. 188 Multiple Cost Communities may indicate the same Point of Insertion. 189 In this case, the Cost Community with the lowest Community-ID is 190 considered first. In other words, all the Cost Communities for a 191 specific Point of Insertion MUST be considered, starting with the one 192 with the lowest Community-ID. 194 If a range of routes is to be aggregated and the resultant aggregates 195 path attributes do not carry the ATOMIC_AGGREGATE attribute, then the 196 resulting aggregate SHOULD have an Extended Communities path 197 attribute which contains the set union of all the Cost Communities 198 from all of the aggregated routes. If multiple Cost Communities for 199 the same Point of Insertion (and with the same Community-ID), then 200 only the ones with the highest Cost SHOULD be included. 202 If the non-transitive version of a Cost Community is received across 203 an Autonomous System boundary, then the receiver SHOULD strip it off 204 the BGP update, and ignore it when running the selection process. 206 5. Deployment Considerations 208 The mechanisms described in this document may be used to modify the 209 BGP path selection process arbitrarily. It is important that a 210 consistent path selection process be maintained across the local 211 Autonomous System to avoid potential routing loops. In other words, 212 if the Cost Community is used, all the nodes in the AS that may have 213 to consider this new community at any Point of Insertion SHOULD be 214 aware of the mechanisms described in this document. 216 6. IANA Considerations 218 IANA is asked to assign the type values indicated in Section 3 to the 219 Cost Community in the BGP Opaque Extended Community registry 220 [BGP_EXT]. 222 Section 3 also defines a series of values to be used to indicate 223 steps in the best path selection process that do not map directly to 224 a path attribute. IANA is expected to maintain a registry for the 225 Cost Community Point of Insertion values. Values 1 through 127 are 226 to be assigned using the "Standards Action" policy or the Early 227 Allocation process [RFC4020]. Values 128 through 191 are to be 228 assigned using the "IETF Consensus" policy. Values 192 through 254 229 are to be assigned using the "First Come First Served" policy. 230 Values 0 and 255 are reserved for future use and SHOULD NOT be used. 231 All the policies mentioned are documented in [RFC5226]. 233 Some of the values in this new registry match the values assigned in 234 the BGP Path Attributes registry [BGP_PAR]. It is RECOMMENDED that 235 an effort be made to assign the same values in both tables when 236 applicable. The table in Appendix A shows the initial allocations 237 for the new Cost Community Point of Insertion registry. 239 7. Security Considerations 241 This document introduces no new security concerns to BGP or other 242 specifications referenced in this document. 244 8. Acknowledgements 246 The authors would like to thank Chris Whyte, Khamsa Enaya, John 247 Scudder, Tom Barron, Eric Rosen, Barry Friedman, Gargi Nalawade, 248 Ruchi Kapoor, Chandra Appanna, Keyur Patel and Pradosh Mohapatra for 249 their comments and suggestions. We would like to also thank Dan 250 Tappan for the Opaque Extended Community type. 252 9. References 253 9.1. Normative References 255 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 256 Requirement Levels", BCP 14, RFC 2119, March 1997. 258 [RFC4020] Kompella, K. and A. Zinin, "Early IANA Allocation of 259 Standards Track Code Points", BCP 100, RFC 4020, 260 February 2005. 262 [RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended 263 Communities Attribute", RFC 4360, February 2006. 265 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 266 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 267 May 2008. 269 9.2. Informative References 271 [BGP_EXT] Internet Assigned Numbers Authority, "BGP Extended 272 Communities", 2010, 273 . 276 [BGP_PAR] Internet Assigned Numbers Authority, "BGP Parameters", 277 2010, . 279 [RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway 280 Protocol 4 (BGP-4)", RFC 4271, January 2006. 282 [RFC4456] Bates, T., Chen, E., and R. Chandra, "BGP Route 283 Reflection: An Alternative to Full Mesh Internal BGP 284 (IBGP)", RFC 4456, April 2006. 286 Appendix A. Cost Community Point of Insertion Registry 288 The tables below document the initial Cost Community Point of 289 Insertion Registry 291 +---------+-------------------------+ 292 | Range | Registration Procedure | 293 +---------+-------------------------+ 294 | 0 | Reserved | 295 | 1-127 | Standards Action | 296 | 128-191 | IETF Consensus | 297 | 192-254 | First Come First Served | 298 | 255 | Reserved | 299 +---------+-------------------------+ 300 Registration Procedure 302 +--------+-------------------+--------------------------------+ 303 | Value | Code | Reference | 304 +--------+-------------------+--------------------------------+ 305 | 1 | ORIGIN | RFC4271 | 306 | 2 | AS_PATH | RFC4271 | 307 | 3 | Unassigned | | 308 | 4 | MULTI_EXIT_DISC | RFC4271 | 309 | 5 | LOCAL_PREF | RFC4271 | 310 | 6-25 | Unassigned | | 311 | 26 | AIGP | draft-ietf-idr-aigp | 312 | 27-127 | Unassigned | | 313 | 128 | ABSOLUTE_VALUE | draft-ietf-idr-custom-decision | 314 | 129 | IGP_COST | draft-ietf-idr-custom-decision | 315 | 130 | EXTERNAL_INTERNAL | draft-ietf-idr-custom-decision | 316 | 131 | BGP_ID | draft-ietf-idr-custom-decision | 317 +--------+-------------------+--------------------------------+ 319 Point of Insertion Codes 321 Authors' Addresses 323 Alvaro Retana 324 Hewlett-Packard Co. 325 2610 Wycliff Road 326 Raleigh, NC 27607 327 USA 329 Email: alvaro.retana@hp.com 331 Russ White 332 Cisco Systems, Inc. 333 7025 Kit Creek Rd. 334 Research Triangle Park, NC 27709 335 USA 337 Email: russwh@cisco.com