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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 5226 (Obsoleted by RFC 8126) Summary: 1 error (**), 0 flaws (~~), 1 warning (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group B. Decraene 3 Internet-Draft Orange 4 Updates: 6790 (if approved) K. Kompella 5 Intended status: Standards Track Juniper Networks, Inc. 6 Expires: December 18, 2017 W. Henderickx 7 Nokia 8 June 16, 2017 10 BGP Next-Hop dependant capabilities 11 draft-ietf-idr-next-hop-capability-00 13 Abstract 15 RFC 5492 defines capabilities advertisement for the BGP peer. In 16 addition, it is useful to be able to advertise BGP Next-Hop dependant 17 capabilities, in particular for forwarding plane features. RFC 5492 18 is not applicable because the BGP peer may be different from the BGP 19 Next-Hop, in particular when BGP Route Reflection is used. This 20 document defines a mechanism to advertise such BGP Next Hop dependant 21 Capabilities. 23 This document defines a new BGP non-transitive attribute to carry 24 Next-Hop Capabilities. This attribute is deleted or possibly 25 modified when the BGP Next Hop is changed. 27 This document also defines a Next-Hop capability to advertise the 28 ability to handle the MPLS Entropy Label defined in RFC 6790. It 29 updates RFC 6790 with regard to this BGP signaling. 31 Requirements Language 33 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 34 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 35 document are to be interpreted as described in RFC 2119 [RFC2119]. 37 Status of This Memo 39 This Internet-Draft is submitted in full conformance with the 40 provisions of BCP 78 and BCP 79. 42 Internet-Drafts are working documents of the Internet Engineering 43 Task Force (IETF). Note that other groups may also distribute 44 working documents as Internet-Drafts. The list of current Internet- 45 Drafts is at http://datatracker.ietf.org/drafts/current/. 47 Internet-Drafts are draft documents valid for a maximum of six months 48 and may be updated, replaced, or obsoleted by other documents at any 49 time. It is inappropriate to use Internet-Drafts as reference 50 material or to cite them other than as "work in progress." 52 This Internet-Draft will expire on December 18, 2017. 54 Copyright Notice 56 Copyright (c) 2017 IETF Trust and the persons identified as the 57 document authors. All rights reserved. 59 This document is subject to BCP 78 and the IETF Trust's Legal 60 Provisions Relating to IETF Documents 61 (http://trustee.ietf.org/license-info) in effect on the date of 62 publication of this document. Please review these documents 63 carefully, as they describe your rights and restrictions with respect 64 to this document. Code Components extracted from this document must 65 include Simplified BSD License text as described in Section 4.e of 66 the Trust Legal Provisions and are provided without warranty as 67 described in the Simplified BSD License. 69 Table of Contents 71 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 72 2. BGP Next-Hop dependant Capabilities Attribute . . . . . . . . 3 73 2.1. Encoding . . . . . . . . . . . . . . . . . . . . . . . . 3 74 2.2. Attribute Operation . . . . . . . . . . . . . . . . . . . 4 75 2.3. Capability Code Operation . . . . . . . . . . . . . . . . 5 76 2.4. Attribute Error Handling . . . . . . . . . . . . . . . . 5 77 3. Entropy Label Next-Hop dependant Capability . . . . . . . . . 6 78 3.1. Entropy Label Next-Hop Capability error handling . . . . 7 79 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 80 4.1. Next-Hop Capabilities Attribute . . . . . . . . . . . . . 7 81 4.2. Next-Hop Capability registry . . . . . . . . . . . . . . 7 82 5. Security Considerations . . . . . . . . . . . . . . . . . . . 8 83 6. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 8 84 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 85 7.1. Normative References . . . . . . . . . . . . . . . . . . 8 86 7.2. Informative References . . . . . . . . . . . . . . . . . 9 87 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 89 1. Introduction 91 [RFC5492] defines capabilities advertisement for the BGP peer. In 92 addition, it is useful to be able to advertise BGP Next-Hop dependant 93 capabilities, in particular for forwarding plane features. RFC 5492 94 is not applicable because the BGP peer may be different from the BGP 95 Next-Hop, in particular when BGP Route Reflection is used. This 96 document defines a mechanism to advertise such BGP Next Hop 97 Capabilities. 99 This document defines a new BGP non-transitive attribute to carry 100 Next-Hop Capabilities. When the BGP Next Hop is changed, this 101 attribute is deleted or possibly modified to take into account the 102 capabilities of the new BGP Next-Hop. Hence it allows advertising 103 capabilities which are dependent of the BGP Next-Hop. 105 This attribute advertises the capabilities of the BGP Next-Hop for 106 the NLRI advertised in the same BGP update. A BGP Next-Hop may 107 advertise different capabilities for different set of NLRI. 109 This document also defines a first application to advertise the 110 capability to handle the MPLS Entropy Label defined in [RFC6790]. 111 Note that RFC 6790 had originally defined a BGP attribute for this 112 but it has been latter deprecated in [RFC7447]. 114 2. BGP Next-Hop dependant Capabilities Attribute 116 2.1. Encoding 118 The BGP Next-Hop dependant Capabilities Attribute is an optional, 119 non-transitive BGP Attribute, of value TBD1. The attribute consists 120 of a set of Next-Hop Capabilities. 122 The inclusion of a Next-Hop Capability "X" in a BGP UPDATE message, 123 indicates that the BGP Next-Hop, encoded in either the NEXT_HOP 124 attribute defined in [RFC4271] or the Network Address of Next Hop 125 field of the MP_REACH_NLRI attribute defined in [RFC4760], supports 126 the capability "X" for the NLRI advertised in this BGP UPDATE. 128 This document does not make a distinction between these two Next-Hop 129 fields and uses the term 'BGP Next-Hop' to refer to whichever one is 130 used in a given BGP UPDATE message. 132 A Next-Hop Capability is a triple (Capability Code, Capability 133 Length, Capability Value) aka a TLV: 135 +------------------------------+ 136 | Capability Code (1 octet) | 137 +------------------------------+ 138 | Capability Length (1 octet) | 139 +------------------------------+ 140 | Capability Value (variable) | 141 ~ ~ 142 +------------------------------+ 144 Figure 1: BGP Next-Hop Capability 146 Capability Code: a one-octet unsigned binary integer which indicates 147 the type of "Next-Hop Capability" advertised and unambiguously 148 identifies an individual capability. 150 Capability Length: a one-octet unsigned binary integer which 151 indicates the length, in octets, of the Capability Value field. A 152 length of 0 indicates that no Capability Value Field is present. 154 Capability Value: a variable-length field from 0 to 255 octets. It 155 is interpreted according to the value of the Capability Code. 157 BGP speakers SHOULD NOT include more than one instance of a Next-Hop 158 capability with the same Capability Code, Capability Length, and 159 Capability Value. Note, however, that processing of multiple 160 instances of such capability does not require special handling, as 161 additional instances do not change the meaning of the announced 162 capability; thus, a BGP speaker MUST be prepared to accept such 163 multiple instances. 165 BGP speakers MAY include more than one instance of a capability (as 166 identified by the Capability Code) with non-zero Capability Length 167 field, but with different Capability Value and either the same or 168 different Capability Length. Processing of these capability 169 instances is specific to the Capability Code and MUST be described in 170 the document introducing the new capability. 172 2.2. Attribute Operation 174 The BGP Next-Hop dependant Capabilities attribute being non- 175 transitive, as per [RFC4271], a BGP speaker which does not understand 176 it will quietly ignore it and not pass it along to other BGP peers. 178 A BGP speaker that understands the BGP Next-Hop dependant 179 Capabilities Attribute and does not change the BGP Next-Hop, SHOULD 180 NOT change the BGP Next-Hop dependant Capabilities Attribute and 181 SHOULD pass the attribute unchanged along to other BGP peers. 183 A BGP speaker that understands the BGP Next-Hop dependant 184 Capabilities Attribute and changes the BGP Next-Hop, MUST remove the 185 received BGP Next-Hop dependant Capabilities Attribute before 186 propagating the BGP UPDATE to other BGP peers. It MAY attach a new 187 BGP Next-Hop dependant Capabilities attribute describing the 188 capabilities of the new BGP Next-Hop for these NLRIs. 190 2.3. Capability Code Operation 192 A BGP speaker receiving a BGP Next-Hop Capability Code that it 193 supports behave as defined in the document defining this Capability 194 Code. A BGP speaker receiving a BGP Next-Hop Capability Code that it 195 does not support MUST ignore this BGP Next-Hop Capability Code. In 196 particular, this MUST NOT be handled as an error. In both cases, the 197 BGP speaker MUST examine the remaining BGP Next-Hop Capability 198 Code(s) that may be present in the BGP Next-Hop Capabilities 199 Attribute. 201 The BGP Next-Hop Capability Code MUST reflect the capability of the 202 router indicated in the BGP Next-Hop, for the NLRI advertised in the 203 BGP UPDATE. If a BGP speaker sets the BGP Next-Hop to an address of 204 a different router (e.g. R), it MUST NOT advertise BGP Next-Hop 205 Capabilities not supported by this router R for these NLRI. 207 The presence of a Next-Hop Capability SHOULD NOT influence route 208 selection or route preference of a route, unless tunneling is used to 209 reach the BGP Next-Hop or the selected route has been learnt from 210 EBGP (i.e. the Next-Hop is in a different AS). Indeed, it is in 211 general impossible for a node to know that all BGP routers of the 212 Autonomous System (AS) will understand a given Next-Hop Capability; 213 and having different routers, within an AS, use a different 214 preference for a route, may result in forwarding loops if tunnelling 215 is not used to reach the BGP Next-Hop. 217 An implementations MAY allow, by configuration, removing this 218 attribute or specific Next-Hop capabilities when advertising the 219 routes over EBGP. 221 2.4. Attribute Error Handling 223 A BGP Next-Hop dependant Capabilities Attribute is considered 224 malformed if the length of the Attribute is not equal to the sum of 225 all (BGP Next-Hop dependant Capability Length +2) of the capabilities 226 carried in this attribute. Note that "2" is the length of the fields 227 "Type" and "Length" of each BGP Next Hop dependant Capability, as the 228 capability length only account for the length of the Value field. 230 A document that specifies a new Next-Hop Capability SHOULD provide 231 specifics regarding what constitutes an error for that Next-Hop 232 Capability. 234 A BGP UPDATE message with a malformed BGP Next-Hop dependant 235 Capabilities Attribute SHALL be handled using the approach of 236 "attribute discard" defined in [RFC7606]. 238 Unknown Next-Hop Capabilities Codes MUST NOT be considered as an 239 error. They MUST be silently ignored. 241 If a Next-Hop dependant Capability is malformed, this Next-Hop 242 Capability Type MUST be ignored. Others Next-Hop Capabilities MUST 243 be processed as usual. 245 3. Entropy Label Next-Hop dependant Capability 247 The Entropy Label Next-Hop Capability has type code 1 and a length of 248 0 or 1 octet. 250 The inclusion of the "Entropy Label" Next-Hop Capability indicates 251 that the BGP Next-Hop can be sent packets, for all routes indicated 252 in the NRLI, with a MPLS entropy label (ELI, EL) added immediately 253 after the label stack advertised with the NLRI. 255 On the receiving side, suppose BGP speaker S has determined that 256 packet P is to be forwarded according to BGP route R, where R is a 257 route of one of the labeled address families. And suppose that L is 258 the label stack embedded in the NLRI of route R. Then to forward 259 packet P according to route R, S either replaces P's top label with 260 L, or else pushes L onto the MPLS label stack. If the EL-Capability 261 is advertised in the BGP UPDATE advertising this route R, S knows 262 that it may safely place the ELI and an EL on the label stack 263 immediately beneath L. 265 A BGP speaker S that sends an UPDATE with the BGP Next-Hop "NH" MAY 266 include the Entropy Label Next-Hop Capability only if the NLRI are 267 labelled and for all the NLRI in the BGP UPDATE, either of the 268 following is true: 270 o Egress case: NH is the egress of the LSP advertised with the NLRI 271 and its capable of handling the ELI during the lookup of the MPLS 272 top label. 274 o Transit LSR case: NH is a transit LSR for the LSP advertised with 275 the NLRI (i.e. NH swaps one of the label advertised in the NLRI) 276 and next downstream BGP Next-Hop(s) has(have) advertised the 277 Entropy Label Next-Hop Capability (or a similar capability 278 signalled by protocol P if the route is redistributed, by NH, from 279 protocol P to BGP). 281 3.1. Entropy Label Next-Hop Capability error handling 283 If the Entropy Label Next-Hop Capability is present more than once, 284 it MUST be considered as received once with a length of 0. 286 If the Entropy Label Next-Hop Capability is received with a length 287 other than 0 or 1, it is not considered malformed, but its semantics 288 are exactly the same as if it had a length of 1. In other words, 289 additional octets MUST be ignored. This is to allow for graceful 290 future extension. 292 4. IANA Considerations 294 4.1. Next-Hop Capabilities Attribute 296 IANA is requested to allocate a new Path Attribute, called "Next-Hop 297 Capabilities", type Code TBD1, from the "BGP Path Attributes" 298 registry. 300 4.2. Next-Hop Capability registry 302 The IANA is requested to create and maintain a registry entitled 303 "Next-Hop Capabilities". 305 The registration policies [RFC5226] for this registry are: 307 1-63 IETF Review 308 64-127 First Come First Served 309 128-250 Standards Action 310 251-254 Experimental Use 311 255 Reserved 313 IANA is requested to make the following initial assignments: 315 Registry Name: Next-Hop Capability. 317 Value Meaning Reference 318 ---------- ---------------------------------------- --------- 319 0 Reserved (not to be allocated) This document 320 1 Entropy Label This document 321 2-250 Unassigned 322 251-254 Experimental This document 323 255 Reserved (for futur registry extension) This document 325 5. Security Considerations 327 This document does not introduce new security vulnerabilities in BGP. 328 Specifically, an operator who is relying on the information carried 329 in BGP must have a transitive trust relationship back to the source 330 of the information. Specifying the mechanism(s) to provide such a 331 relationship is beyond the scope of this document. Please refer to 332 the Security Considerations section of [RFC4271] for security 333 mechanisms applicable to BGP. 335 6. Acknowledgement 337 The Entropy Label Next-Hop Capability defined in this document is 338 based on the ELC BGP attribute defined in section 5.2 of [RFC6790]. 340 The authors wish to thank John Scudder for the discussions on this 341 topic and Eric Rosen for his in-depth review of this document. 343 The authors wish to thank Jie Dong for his review and comments. 345 7. References 347 7.1. Normative References 349 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 350 Requirement Levels", BCP 14, RFC 2119, 351 DOI 10.17487/RFC2119, March 1997, 352 . 354 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 355 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 356 DOI 10.17487/RFC4271, January 2006, 357 . 359 [RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter, 360 "Multiprotocol Extensions for BGP-4", RFC 4760, 361 DOI 10.17487/RFC4760, January 2007, 362 . 364 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 365 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 366 DOI 10.17487/RFC5226, May 2008, 367 . 369 [RFC6790] Kompella, K., Drake, J., Amante, S., Henderickx, W., and 370 L. Yong, "The Use of Entropy Labels in MPLS Forwarding", 371 RFC 6790, DOI 10.17487/RFC6790, November 2012, 372 . 374 [RFC7606] Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and K. 375 Patel, "Revised Error Handling for BGP UPDATE Messages", 376 RFC 7606, DOI 10.17487/RFC7606, August 2015, 377 . 379 7.2. Informative References 381 [RFC5492] Scudder, J. and R. Chandra, "Capabilities Advertisement 382 with BGP-4", RFC 5492, DOI 10.17487/RFC5492, February 383 2009, . 385 [RFC7447] Scudder, J. and K. Kompella, "Deprecation of BGP Entropy 386 Label Capability Attribute", RFC 7447, 387 DOI 10.17487/RFC7447, February 2015, 388 . 390 Authors' Addresses 392 Bruno Decraene 393 Orange 395 Email: bruno.decraene@orange.com 397 Kireeti Kompella 398 Juniper Networks, Inc. 399 1194 N. Mathilda Avenue 400 Sunnyvale, CA 94089 401 USA 403 Email: kireeti.kompella@gmail.com 405 Wim Henderickx 406 Nokia 407 Copernicuslaan 50 408 Antwerp 2018, CA 95134 409 Belgium 411 Email: wim.henderickx@nokia.com