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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 L2VPN Workgroup Ali Sajassi 3 INTERNET-DRAFT Samer Salam 4 Intended Status: Standards Track Sami Boutros 5 Cisco 7 Wim Henderickx 8 Alcatel-Lucent 10 Jim Uttaro 11 AT&T 13 Aldrin Isaac 14 Bloomberg 16 Expires: April 21, 2014 October 21, 2013 18 E-TREE Support in EVPN & PBB-EVPN 19 draft-sajassi-l2vpn-evpn-etree-02 21 Abstract 23 The Metro Ethernet Forum (MEF) has defined a rooted-multipoint 24 Ethernet service known as Ethernet Tree (E-Tree). [ETREE-FMWK] 25 proposes a solution framework for supporting this service in MPLS 26 networks. This document discusses how those functional requirements 27 can be easily met with EVPN. 29 Status of this Memo 31 This Internet-Draft is submitted to IETF in full conformance with the 32 provisions of BCP 78 and BCP 79. 34 Internet-Drafts are working documents of the Internet Engineering 35 Task Force (IETF), its areas, and its working groups. Note that 36 other groups may also distribute working documents as 37 Internet-Drafts. 39 Internet-Drafts are draft documents valid for a maximum of six months 40 and may be updated, replaced, or obsoleted by other documents at any 41 time. It is inappropriate to use Internet-Drafts as reference 42 material or to cite them other than as "work in progress." 44 The list of current Internet-Drafts can be accessed at 45 http://www.ietf.org/1id-abstracts.html 46 The list of Internet-Draft Shadow Directories can be accessed at 47 http://www.ietf.org/shadow.html 49 Copyright and License Notice 51 Copyright (c) 2013 IETF Trust and the persons identified as the 52 document authors. All rights reserved. 54 This document is subject to BCP 78 and the IETF Trust's Legal 55 Provisions Relating to IETF Documents 56 (http://trustee.ietf.org/license-info) in effect on the date of 57 publication of this document. Please review these documents 58 carefully, as they describe your rights and restrictions with respect 59 to this document. Code Components extracted from this document must 60 include Simplified BSD License text as described in Section 4.e of 61 the Trust Legal Provisions and are provided without warranty as 62 described in the Simplified BSD License. 64 Table of Contents 66 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 67 1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3 68 2 E-Tree Scenarios and EVPN / PBB-EVPN Support . . . . . . . . . 3 69 2.1 Scenario 1: Leaf OR Root site(s) per PE . . . . . . . . . . 3 70 2.2 Scenario 2: Leaf AND Root site(s) per PE . . . . . . . . . . 4 71 2.3 Scenario 3: Leaf AND Root site(s) per Ethernet Segment . . . 4 72 3 Operation for EVPN . . . . . . . . . . . . . . . . . . . . . . . 5 73 3.1 Known Unicast Traffic . . . . . . . . . . . . . . . . . . . 5 74 3.2 BUM Traffic . . . . . . . . . . . . . . . . . . . . . . . . 6 75 3.3 E-TREE Traffic Flows for EVPN . . . . . . . . . . . . . . . 7 76 3.3.1 E-Tree with MAC Learning . . . . . . . . . . . . . . . . 7 77 3.3.2 E-Tree without MAC Learning . . . . . . . . . . . . . . 8 78 4 Operation for PBB-EVPN . . . . . . . . . . . . . . . . . . . . . 8 79 4.1 Known Unicast Traffic . . . . . . . . . . . . . . . . . . . 9 80 4.2 BUM Traffic . . . . . . . . . . . . . . . . . . . . . . . . 9 81 5 Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . . 10 82 6 Security Considerations . . . . . . . . . . . . . . . . . . . . 10 83 7 IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 10 84 8 References . . . . . . . . . . . . . . . . . . . . . . . . . . 10 85 8.1 Normative References . . . . . . . . . . . . . . . . . . . 10 86 8.2 Informative References . . . . . . . . . . . . . . . . . . 10 87 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10 89 1 Introduction 91 The Metro Ethernet Forum (MEF) has defined a rooted-multipoint 92 Ethernet service known as Ethernet Tree (E-Tree). In an E-Tree 93 service, endpoints are labeled as either Root or Leaf sites. Root 94 sites can communicate with all other sites. Leaf sites can 95 communicate with Root sites but not with other Leaf sites. 97 [ETREE-FMWK] proposes the solution framework for supporting E-Tree 98 service in MPLS networks. The document identifies the functional 99 components of the overall solution to emulate E-Tree services in 100 addition to Ethernet LAN (E-LAN) services on an existing MPLS 101 network. 103 [EVPN] is a solution for multipoint L2VPN services, with advanced 104 multi-homing capabilities, using BGP for distributing customer/client 105 MAC address reach-ability information over the MPLS/IP network. [PBB- 106 EVPN] combines the functionality of EVPN with [802.1ah] Provider 107 Backbone Bridging for MAC address scalability. 109 This document discusses how the functional requirements for E-Tree 110 service can be easily met with EVPN and PBB-EVPN. 112 1.1 Terminology 114 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 115 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 116 document are to be interpreted as described in RFC 2119 [KEYWORDS]. 118 2 E-Tree Scenarios and EVPN / PBB-EVPN Support 120 In this section, we will categorize support for E-Tree into three 121 different scenarios, depending on the nature of the site association 122 (Root/Leaf) per PE or per Ethernet Segment: 124 - Leaf OR Root site(s) per PE 126 - Leaf AND Root site(s) per PE 128 - Leaf AND Root site(s) per Ethernet Segment 130 2.1 Scenario 1: Leaf OR Root site(s) per PE 132 In this scenario, a PE may have Root sites OR Leaf sites for a given 133 VPN instance, but not both concurrently. The PE may have both Root 134 and Leaf sites albeit for different VPNs. Every Ethernet Segment 135 connected to the PE is uniquely identified as either a Root or a Leaf 136 site. 138 +---------+ +---------+ 139 | PE1 | | PE2 | 140 +---+ | +---+ | +------+ | +---+ | +---+ 141 |CE1+-----ES1----+--+ | | | MPLS | | | +--+----ES2-----+CE2| 142 +---+ (Root) | | E | | | /IP | | | E | | (Leaf) +---+ 143 | | V | | | | | | V | | 144 | | I | | | | | | I | | +---+ 145 | | | | | | | | +--+----ES3-----+CE3| 146 | +---+ | +------+ | +---+ | (Leaf) +---+ 147 +---------+ +---------+ 149 Figure 1: Scenario 1 151 2.2 Scenario 2: Leaf AND Root site(s) per PE 153 In this scenario, a PE may have a set of one or more Root sites AND a 154 set of one or more Leaf sites for a given VPN instance. Every 155 Ethernet Segment connected to the PE is uniquely identified as either 156 a Root or a Leaf site. 158 +---------+ +---------+ 159 | PE1 | | PE2 | 160 +---+ | +---+ | +------+ | +---+ | +---+ 161 |CE1+-----ES1----+--+ | | | | | | +--+----ES2-----+CE2| 162 +---+ (Leaf) | | E | | | MPLS | | | E | | (Leaf) +---+ 163 | | V | | | /IP | | | V | | 164 | | I | | | | | | I | | +---+ 165 | | | | | | | | +--+----ES3-----+CE3| 166 | +---+ | +------+ | +---+ | (Root) +---+ 167 +---------+ +---------+ 169 Figure 2: Scenario 2 171 2.3 Scenario 3: Leaf AND Root site(s) per Ethernet Segment 173 In this scenario, a PE may have a set of one or more Root sites AND a 174 set of one or more Leaf sites for a given VPN instance. An Ethernet 175 Segment connected to the PE may be identified as both a Root and a 176 Leaf site concurrently. 178 +---------+ +---------+ 179 | PE1 | | PE2 | 180 +---+ | +---+ | +------+ | +---+ | +---+ 181 |CE1+-----ES1----+--+ | | | | | | +--+----ES2-----+CE2| 182 +---+ (Leaf/Root)| | E | | | MPLS | | | E | | (Leaf/Root)+---+ 183 | | V | | | /IP | | | V | | 184 | | I | | | | | | I | | +---+ 185 | | | | | | | | +--+----ES3-----+CE3| 186 | +---+ | +------+ | +---+ | (Leaf) +---+ 187 +---------+ +---------+ 189 Figure 3: Scenario 3 191 3 Operation for EVPN 193 [EVPN] defines the notion of an Ethernet Segment which can be readily 194 used to identify a Root and/or Leaf site in E-TREE services. In other 195 words, [EVPN] has inherent capability to support E-TREE services 196 without defining any new BGP routes. It only requires a minor 197 modification to the existing procedures and a modification to a BGP 198 attribute as shown in this section. 200 The following procedures are used consistently for all the scenarios 201 highlighted in the previous section. 203 3.1 Known Unicast Traffic 205 For known unicast traffic, the PE must advertise a Root/Leaf 206 indication along with each MAC Advertisement route, to indicate 207 whether the associated MAC address was learnt from a Root or a Leaf. 208 This enables remote PEs to perform ingress filtering for known 209 unicast traffic: On the ingress PE, the MAC destination address 210 lookup yields, in addition to the forwarding adjacency, a flag which 211 indicates whether the target MAC is associated with a Root or a Leaf 212 site. The ingress PE cross-checks this flag with the status of the 213 originating site, and if both are a Leaf, then the packet is not 214 forwarded. 216 The PE places all Leaf Ethernet Segments of a given bridge domain in 217 a single split-horizon group in order to prevent intra-PE forwarding 218 among Leaf segments. This split-horizon function applies to BUM 219 traffic as well. 221 To support the above ingress filtering functionality, a new Root/Leaf 222 indication flag will added to the Tunnel Encapsulation Type Extended 223 Community [RFC5512]. This extended community will be advertised with 224 each EVPN MAC Advertisement route. 226 3.2 BUM Traffic 228 For BUM traffic, it is not possible to perform filtering on the 229 ingress PE, as is the case with known unicast, because of the multi- 230 destination nature of the traffic. As such, the solution relies on 231 egress filtering. In order to apply the proper egress filtering, 232 which varies based on whether a packet is sent from a Root or a Leaf, 233 the MPLS-encapsulated frames MUST be tagged with an indication of 234 whether they originated from a Root or a Leaf Ethernet Segment. This 235 can be achieved in EVPN through the use of the ESI MPLS label, since 236 this label identifies the Ethernet Segment of origin of a given 237 frame. The egress PE determines whether or not to forward a 238 particular frame to an Ethernet Segment depending on the split- 239 horizon rule defined in [EVPN]: 241 - If the ESI Label indicates that the source Ethernet Segment is a 242 Root, then the frame can be forwarded on a segment granted that it 243 passes the split-horizon check. 245 - If the ESI Label indicates that the source Ethernet Segment is a 246 Leaf, then the frame can be forwarded only on a Root segment, granted 247 that it passes the split-horizon check. 249 When advertising the ESI MPLS label for a given Ethernet Segment, a 250 PE must indicate whether the corresponding ESI is a Root or a Leaf 251 site. This can be done by encoding the Root or Leaf indication in the 252 Flags field of the ESI MPLS label Extended Community attribute 253 ([EVPN] Section 8) to indicate Root/Leaf status. 255 In the case where a multi-homed Ethernet Segment has both Root and 256 Leaf sites attached, two ESI MPLS labels are allocated and 257 advertised: one ESI MPLS label denotes Root and the other denotes 258 Leaf. The ingress PE imposes the right ESI MPLS label depending on 259 whether the Ethernet frame originated from the Root or Leaf site on 260 that Ethernet Segment. The mechanism by which the PE identifies 261 whether a given frame originated from a Root or Leaf site on the 262 segment is based on the Ethernet Tag associated with the frame. Other 263 mechanisms of identification, beyond the Ethernet Tag, are outside 264 the scope of this document. It should be noted that support for both 265 Root and Leaf sites on a single Ethernet Segment requires that the PE 266 performs the Ethernet Segment split-horizon check on a per Ethernet 267 Tag basis. In the case where a multi-homed Ethernet Segment has 268 either Root or Leaf sites attached, then a single ESI MPL label is 269 allocated and advertised. 271 Furthermore, a PE advertises two special ESI MPLS labels: one for 272 Root and another for Leaf. These are used by remote PEs for traffic 273 originating from single-homed segments and for multi-homed segments 274 that are not connected to the advertising PE. Note that these special 275 labels are advertised on a per PE basis (i.e. each PE advertises only 276 two such special labels). 278 In addition to egress filtering (which is a MUST requirement), an 279 EVPN PE implementation MAY provide topology constraint among the PEs 280 belonging to the same EVI associated with an E-TREE service. The 281 purpose of this topology constraint is to avoid having PEs with only 282 host Leaf sites importing and processing BGP MAC routes from each 283 other, thereby unnecessarily exhausting their RIB tables. However, as 284 soon as a Root site is added to a Leaf PE, then that PE needs to 285 process MAC routes from all other Leaf PEs and add them to its 286 forwarding table. To support such topology constrain in EVPN, two BGP 287 Route-Targets (RTs) are used for every EVPN Instance (EVI): one RT is 288 associated with the Root sites and the other is associated with the 289 Leaf sites. On a per EVI basis, every PE exports the single RT 290 associated with its type of site(s). Furthermore, a PE with Root 291 site(s) imports both Root and Leaf RTs, whereas a PE with Leaf 292 site(s) only imports the Root RT. If for a given EVI, the PEs can 293 eventually have both Leaf and Root sites attached, even though they 294 may start as Root-only or Leaf-only PEs, then it is recommended to 295 use a single RT per EVI and avoid additional configuration and 296 operational overhead. If the number of EVIs is very large (e.g., more 297 than 32K or 64K), then RT type 0 as defined in [RFC4360] SHOULD be 298 used; otherwise, RT type 2 is sufficient. 300 3.3 E-TREE Traffic Flows for EVPN 302 Per [ETREE-FMWK], a generic E-Tree service supports all of the 303 following traffic flows: 305 - Ethernet Unicast from Root to Roots & Leaf 306 - Ethernet Unicast from Leaf to Root 307 - Ethernet Broadcast/Multicast from Root to Roots & Leafs 308 - Ethernet Broadcast/Multicast from Leaf to Roots 310 A particular E-Tree service may need to support all of the above 311 types of flows or only a select subset, depending on the target 312 application. In the case where unicast flows need not be supported, 313 the L2VPN PEs can avoid performing any MAC learning function. 315 In the subsections that follow, we will describe the operation of 316 EVPN to support E-Tree service with and without MAC learning. 318 3.3.1 E-Tree with MAC Learning 320 The PEs implementing an E-Tree service must perform MAC learning when 321 unicast traffic flows must be supported from Root to Leaf or from 322 Leaf to Root sites. In this case, the PE with Root sites performs MAC 323 learning in the data-path over the Ethernet Segments, and advertises 324 reachability in EVPN MAC Advertisement routes. These routes will be 325 imported by PEs that have Leaf sites as well as by PEs that have Root 326 sites, in a given EVI. Similarly, the PEs with Leaf sites perform MAC 327 learning in the data-path over their Ethernet Segments, and advertise 328 reachability in EVPN MAC Advertisement routes which are imported only 329 by PEs with at least one Root site in the EVI. A PE with only Leaf 330 sites will not import these routes. PEs with Root and/or Leaf sites 331 may use the Ethernet A-D routes for aliasing (in the case of multi- 332 homed segments) and for mass MAC withdrawal. 334 To support multicast/broadcast from Root to Leaf sites, either a P2MP 335 tree rooted at the PE(s) with the Root site(s) or ingress replication 336 can be used. The multicast tunnels are set up through the exchange of 337 the EVPN Inclusive Multicast route, as defined in [EVPN]. 339 To support multicast/broadcast from Leaf to Root sites, ingress 340 replication should be sufficient for most scenarios where there is a 341 single Root or few Roots. If the number of Roots is large, a P2MP 342 tree rooted at the PEs with Leaf sites may be used. 344 3.3.2 E-Tree without MAC Learning 346 The PEs implementing an E-Tree service need not perform MAC learning 347 when the traffic flows between Root and Leaf sites are multicast or 348 broadcast. In this case, the PEs do not exchange EVPN MAC 349 Advertisement routes. Instead, the Ethernet A-D routes are used to 350 exchange the EVPN labels. 352 The fields of the Ethernet A-D route are populated per the procedures 353 defined in [EVPN], and the route import rules are as described in 354 previous sections. 356 4 Operation for PBB-EVPN 358 In PBB-EVPN, the PE must advertise a Root/Leaf indication along with 359 each MAC Advertisement route, to indicate whether the associated B- 360 MAC address corresponds to a Root or a Leaf site. Similar to the EVPN 361 case, this flag will be added to the Tunnel Encapsulation Type 362 Extended Community [RFC5512], and advertised with each MAC 363 Advertisement route. 365 In the case where a multi-homed Ethernet Segment has both Root and 366 Leaf sites attached, two B-MAC addresses are allocated and 367 advertised: one B-MAC address denotes Root and the other denotes 368 Leaf. The ingress PE uses the right B-MAC source address depending on 369 whether the Ethernet frame originated from the Root or Leaf site on 370 that Ethernet Segment. The mechanism by which the PE identifies 371 whether a given frame originated from a Root or Leaf site on the 372 segment is based on the Ethernet Tag associated with the frame. Other 373 mechanisms of identification, beyond the Ethernet Tag, are outside 374 the scope of this document. It should be noted that support for both 375 Root and Leaf sites on a single Ethernet Segment requires that the PE 376 performs the Ethernet Segment split-horizon check on a per Ethernet 377 Tag basis. In the case where a multi-homed Ethernet Segment has 378 either Root or Leaf sites attached, then a single B-MAC address is 379 allocated and advertised per segment. 381 Furthermore, a PE advertises two global B-MAC addresses: one for Root 382 and another for Leaf, and tags them as such in the MAC Advertisement 383 routes. These B-MAC addresses are used as source addresses for 384 traffic originating from single-homed segments. 386 4.1 Known Unicast Traffic 388 For known unicast traffic, the PEs perform ingress filtering: On the 389 ingress PE, the C-MAC destination address lookup yields, in addition 390 to the target B-MAC address and forwarding adjacency, a flag which 391 indicates whether the target B-MAC is associated with a Root or a 392 Leaf site. The ingress PE cross-checks this flag with the status of 393 the originating site, and if both are a Leaf, then the packet is not 394 forwarded. 396 The PE places all Leaf Ethernet Segments of a given bridge domain in 397 a single split-horizon group in order to prevent intra-PE forwarding 398 among Leaf segments. This split-horizon function applies to BUM 399 traffic as well. 401 4.2 BUM Traffic 403 For BUM traffic, the PEs must perform egress filtering. When a PE 404 receives a MAC advertisement route, it updates its Ethernet Segment 405 egress filtering function (based on the B-MAC source address), as 406 follows: 408 - If the MAC Advertisement route indicates that the advertised B-MAC 409 is a Leaf, and the local Ethernet Segment is a Leaf as well, then the 410 source B-MAC address is added to the B-MAC filtering list. 412 - Otherwise, the B-MAC filtering list is not updated. 414 When the egress PE receives the packet, it examines the B-MAC source 415 address to check whether it should filter or forward the frame. Note 416 that this uses the same filtering logic as baseline [PBB-EVPN] and 417 does not require any additional flags in the data-plane. 419 5 Acknowledgement 421 We would like to thank Sami Boutros and Dennis Cai for their 422 comments. 424 6 Security Considerations 426 Same security considerations as [EVPN]. 428 7 IANA Considerations 430 Allocation of Extended Community Type and Sub-Type for EVPN. 432 8 References 434 8.1 Normative References 436 [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate 437 Requirement Levels", BCP 14, RFC 2119, March 1997. 439 [RFC4360] S. Sangli et al, ""BGP Extended Communities Attribute", 440 February, 2006. 442 [RFC5512] Mohapatra, P. and E. Rosen, "The BGP 443 Encapsulation Subsequent Address Family Identifier (SAFI) 444 and the BGP Tunnel Encapsulation Attribute", RFC 5512, 445 April 2009. 447 8.2 Informative References 449 [ETREE-FMWK] Key et al., "A Framework for E-Tree Service over MPLS 450 Network", draft-ietf-l2vpn-etree-frwk-03, work in progress, September 451 2013. 453 [EVPN] Sajassi et al., "BGP MPLS Based Ethernet VPN", draft-ietf- 454 l2vpn-evpn-04.txt, work in progress, July, 2013. 456 [PBB-EVPN] Sajassi et al., "PBB-EVPN", draft-ietf-l2vpn-pbb-evpn- 457 05.txt, work in progress, October, 2013. 459 Authors' Addresses 460 Ali Sajassi 461 Cisco 462 Email: sajassi@cisco.com 464 Samer Salam 465 Cisco 466 Email: ssalam@cisco.com 468 Wim Henderickx 469 Alcatel-Lucent 470 Email: wim.henderickx@alcatel-lucent.com 472 Jim Uttaro 473 AT&T 474 Email: ju1738@att.com 476 Aldrin 477 Bloomberg Issac 478 Email: aisaac71@bloomberg.net 480 Sami Boutros 481 Cisco 482 Email: sboutros@cisco.com