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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 Cisco Systems, Inc. 4 Intended status: Standards Track R. White 5 Expires: May 22, 2014 6 November 18, 2013 8 BGP Custom Decision Process 9 draft-ietf-idr-custom-decision-04 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 22, 2014. 43 Copyright Notice 45 Copyright (c) 2013 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 . . . . . . . . . . . . . . . . . . . . . . . . 2 61 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3 62 3. The BGP Cost Community . . . . . . . . . . . . . . . . . . . 3 63 4. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 4 64 5. Deployment Considerations . . . . . . . . . . . . . . . . . . 5 65 6. Security Considerations . . . . . . . . . . . . . . . . . . . 6 66 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 67 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 68 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 69 9.1. Normative References . . . . . . . . . . . . . . . . . . 6 70 9.2. Informative References . . . . . . . . . . . . . . . . . 7 71 Appendix A. Cost Community Point of Insertion Registry . . . . . 7 72 Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 8 73 B.1. Changes between the -00 and -01 versions. . . . . . . . . 8 74 B.2. Changes between the -01 and -02 versions. . . . . . . . . 8 75 B.3. Changes between the -02 and -03 versions. . . . . . . . . 8 76 B.4. Changes between the -03 and -04 versions. . . . . . . . . 8 77 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 79 1. Introduction 81 There are a number of metrics available within the BGP decision 82 process [RFC4271] which can be used to determine the exit point for 83 traffic, but there is no metric, or combination of metrics, which can 84 be used to break a tie among generally equal paths. 86 o LOCAL_PREF: The LOCAL_PREF is an absolute tie breaker near the 87 beginning of the decision process. There is no way to configure 88 the LOCAL_PREF such that the MED, IGP metric, and other metrics 89 are considered before breaking a tie. 91 o MED: The MULTI_EXIT_DISC is an indicator of which local entrance 92 point an AS would like a peering AS to use; MED isn't suitable to 93 break the tie between two equal cost paths learned from two peer 94 ASes. MED is also compared before the IGP metric; there is no way 95 to set the MED so a path with a higher IGP metric is preferred 96 over a path with a lower IGP metric. 98 o IGP Metric: It is possible, using the IGP metric, to influence 99 individual paths with otherwise equal cost metrics, but only by 100 changing the next hop towards each path, and configuring the IGP 101 costs of reaching each next hop. This method is cumbersome, and 102 prone to confusion and error. 104 The BGP specification defines a Decision Process for installation of 105 routes into the Loc-RIB. This process takes into account an 106 extensive series of path attributes, which can be manipulated to 107 indicate preference for specific paths. It is cumbersome (if at all 108 possible) for the end user to define policies that will select, after 109 partial comparison, a path based on subjective local (domain and/or 110 node) criteria. 112 This document defines a new Extended Community, called the Cost 113 Community, which may be used in tie breaking during the best path 114 selection process. The end result is a custom decision process. 116 2. Requirements Language 118 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 119 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 120 document are to be interpreted as described in [RFC2119]. 122 3. The BGP Cost Community 124 The BGP Cost Community is an Opaque Extended Community [RFC4360] 125 defined as follows: 127 Type Field: 128 The value of the high-order octet of this Opaque Extended 129 Community is 0x03 or 0x43. The value of the low-order octet of 130 the extended type field for this community is 0x01. 132 Value Field: 133 The Value field contains three distinct sub-fields, described 134 below: 136 +------------------------------+ 137 | Point of Insertion (1 octet) | 138 +------------------------------+ 139 | Community-ID (1 octet) | 140 +------------------------------+ 141 | Cost (4 octets) | 142 +------------------------------+ 144 The Point of Insertion sub-field contains the value of the path 145 attribute *after* which this community MUST be considered during 146 the best path selection process. 148 The BGP decision process includes some steps that do not 149 correspond to any path attribute; the following values are 150 defined: 152 128 ABSOLUTE_VALUE - Indicates that the Cost Community MUST be 153 considered as the first step in determining the Degree of 154 Preference of a path. 156 129 IGP_COST - Indicates that the Cost Community MUST be 157 considered after the interior (IGP) distance to the next-hop 158 has been compared. 160 130 EXTERNAL_INTERNAL - Indicates that the Cost Community MUST 161 be considered after the paths advertised by BGP speakers in 162 a neighboring autonomous system (if any) have been selected. 164 131 BGP_ID - Indicates that the Cost Community MUST be 165 considered after the BGP Identifier (or ORIGINATOR_ID 166 [RFC4456]) has been compared. 168 The Community-ID sub-field contains an identifier to distinguish 169 between multiple instances of the Cost Community. The high-order 170 bit is reserved to indicate that the Cost Community MUST replace 171 the path attribute specified by the Point of Insertion during the 172 best path selection process. 174 The Cost sub-field contains a value assigned by the network 175 administrator and that is significant to the local autonomous 176 system. The lower cost MUST be preferred. The default value is 177 0x7FFFFFFF (half the maximum value). 179 4. Operation 180 The network administrator may use the Cost Community to assign a 181 value to a path originated or learned from a peer in any part of the 182 local domain. The Point of Insertion MUST also be specified using 183 the values defined in Appendix A. 185 If a BGP speaker receives a path that contains the Cost Community, it 186 SHOULD consider its value at the Point of Insertion specified, when 187 calculating the best path [RFC4271]. 189 If the Point of Insertion is not valid for the local best path 190 selection implementation, then the Cost Community SHOULD be silently 191 ignored. Paths that do not contain the Cost Community (for a valid, 192 particular Point of Insertion) MUST be considered to have the default 193 value. 195 Multiple Cost Communities may indicate the same Point of Insertion. 196 In this case, the Cost Community with the lowest Community-ID is 197 considered first. In other words, all the Cost Communities for a 198 specific Point of Insertion MUST be considered, starting with the one 199 with the lowest Community-ID. 201 If a range of routes is to be aggregated and the resultant aggregate 202 path attributes do not carry the ATOMIC_AGGREGATE attribute, then the 203 resulting aggregate SHOULD have an Extended Communities path 204 attribute which contains the set union of all the Cost Communities 205 from all of the aggregated routes. If multiple Cost Communities for 206 the same Point of Insertion (and with the same Community-ID) exist, 207 then only the ones with the highest Cost SHOULD be included. 209 If the non-transitive version of a Cost Community is received across 210 an Autonomous System boundary, then the receiver MUST strip it off 211 the BGP update, and ignore it when running the selection process. 213 5. Deployment Considerations 215 The mechanisms described in this document may be used to modify the 216 BGP path selection process arbitrarily. It is important that a 217 consistent path selection process be maintained across the local 218 Autonomous System to avoid potential routing loops. In other words, 219 if the Cost Community is used, all the nodes in the AS that may have 220 to consider this new community at any Point of Insertion SHOULD be 221 aware of the mechanisms described in this document. 223 6. Security Considerations 225 This document introduces no new security concerns to BGP or other 226 specifications referenced in this document. 228 7. IANA Considerations 230 IANA is asked to assign the type values indicated in Section 3 to the 231 Cost Community in the BGP Opaque Extended Community registry 232 [BGP_EXT]. 234 Section 3 also defines a series of values to be used to indicate 235 steps in the best path selection process that do not map directly to 236 a path attribute. IANA is expected to maintain a registry for the 237 Cost Community Point of Insertion values. Values 1 through 127 are 238 to be assigned using the "Standards Action" policy or the Early 239 Allocation process [RFC4020]. Values 128 through 191 are to be 240 assigned using the "IETF Consensus" policy. Values 192 through 254 241 are to be assigned using the "First Come First Served" policy. 242 Values 0 and 255 are reserved for future use and SHOULD NOT be used. 243 All the policies mentioned are documented in [RFC5226]. 245 Some of the values in this new registry match the values assigned in 246 the BGP Path Attributes registry [BGP_PAR]. It is RECOMMENDED that 247 an effort be made to assign the same values in both tables when 248 applicable. The table in Appendix A shows the initial allocations 249 for the new Cost Community Point of Insertion registry. 251 8. Acknowledgements 253 There have been many people who have shown their support and provided 254 valuable input, comments and implementations -- the authors would 255 like to thank all of them! We would like to also thank Dan Tappan 256 for the Opaque Extended Community type. 258 9. References 260 9.1. Normative References 262 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 263 Requirement Levels", BCP 14, RFC 2119, March 1997. 265 [RFC4020] Kompella, K. and A. Zinin, "Early IANA Allocation of 266 Standards Track Code Points", BCP 100, RFC 4020, February 267 2005. 269 [RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended 270 Communities Attribute", RFC 4360, February 2006. 272 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 273 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 274 May 2008. 276 9.2. Informative References 278 [BGP_EXT] Internet Assigned Numbers Authority, "BGP Extended 279 Communities", 2010, . 282 [BGP_PAR] Internet Assigned Numbers Authority, "BGP Parameters", 283 2010, . 285 [RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway 286 Protocol 4 (BGP-4)", RFC 4271, January 2006. 288 [RFC4456] Bates, T., Chen, E., and R. Chandra, "BGP Route 289 Reflection: An Alternative to Full Mesh Internal BGP 290 (IBGP)", RFC 4456, April 2006. 292 Appendix A. Cost Community Point of Insertion Registry 294 The tables below document the initial Cost Community Point of 295 Insertion Registry 297 +---------+-------------------------+ 298 | Range | Registration Procedure | 299 +---------+-------------------------+ 300 | 0 | Reserved | 301 | 1-127 | Standards Action | 302 | 128-191 | IETF Consensus | 303 | 192-254 | First Come First Served | 304 | 255 | Reserved | 305 +---------+-------------------------+ 307 Registration Procedure 309 +--------+-------------------+--------------------------------+ 310 | Value | Code | Reference | 311 +--------+-------------------+--------------------------------+ 312 | 1 | ORIGIN | RFC4271 | 313 | 2 | AS_PATH | RFC4271 | 314 | 3 | Unassigned | | 315 | 4 | MULTI_EXIT_DISC | RFC4271 | 316 | 5 | LOCAL_PREF | RFC4271 | 317 | 6-25 | Unassigned | | 318 | 26 | AIGP | draft-ietf-idr-aigp | 319 | 27-127 | Unassigned | | 320 | 128 | ABSOLUTE_VALUE | draft-ietf-idr-custom-decision | 321 | 129 | IGP_COST | draft-ietf-idr-custom-decision | 322 | 130 | EXTERNAL_INTERNAL | draft-ietf-idr-custom-decision | 323 | 131 | BGP_ID | draft-ietf-idr-custom-decision | 324 +--------+-------------------+--------------------------------+ 326 Point of Insertion Codes 328 Appendix B. Change Log 330 B.1. Changes between the -00 and -01 versions. 332 o Updated authors' contact information. 334 o Editorial changes in the "Operations" and "Acknowledgement" 335 sections. 337 B.2. Changes between the -01 and -02 versions. 339 o Updated authors' contact information. 341 o Added text to replace a step in the selection process. 343 o Minor edits. 345 B.3. Changes between the -02 and -03 versions. 347 o No changes; just a refresh. 349 B.4. Changes between the -03 and -04 versions. 351 o Updated authors' contact information. 353 Authors' Addresses 355 Alvaro Retana 356 Cisco Systems, Inc. 357 7025 Kit Creek Rd. 358 Research Triangle Park, NC 27709 359 USA 361 Email: aretana@cisco.com 363 Russ White 365 Email: russw@riw.us