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Giuliano 4 Updates: 6514 (if approved) Juniper Networks 5 Intended status: Standards Track May 26, 2020 6 Expires: November 27, 2020 8 MVPN and MSDP SA Interoperation 9 draft-ietf-bess-mvpn-msdp-sa-interoperation-05 11 Abstract 13 This document specifies the procedures for interoperation between 14 Multicast Virtual Private Network (MVPN) Source Active routes and 15 customer Multicast Source Discovery Protocol (MSDP) Source Active 16 routes, which is useful for MVPN provider networks offering services 17 to customers with an existing MSDP infrastructure. Without the 18 procedures described in this document, VPN-specific MSDP sessions are 19 required among the PEs that are customer MSDP peers. This document 20 updates RFC6514. 22 Requirements Language 24 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 25 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 26 "OPTIONAL" in this document are to be interpreted as described in BCP 27 14 [RFC2119] [RFC8174] when, and only when, they appear in all 28 capitals, as shown here. 30 Status of This Memo 32 This Internet-Draft is submitted in full conformance with the 33 provisions of BCP 78 and BCP 79. 35 Internet-Drafts are working documents of the Internet Engineering 36 Task Force (IETF). Note that other groups may also distribute 37 working documents as Internet-Drafts. The list of current Internet- 38 Drafts is at https://datatracker.ietf.org/drafts/current/. 40 Internet-Drafts are draft documents valid for a maximum of six months 41 and may be updated, replaced, or obsoleted by other documents at any 42 time. It is inappropriate to use Internet-Drafts as reference 43 material or to cite them other than as "work in progress." 45 This Internet-Draft will expire on November 27, 2020. 47 Copyright Notice 49 Copyright (c) 2020 IETF Trust and the persons identified as the 50 document authors. All rights reserved. 52 This document is subject to BCP 78 and the IETF Trust's Legal 53 Provisions Relating to IETF Documents 54 (https://trustee.ietf.org/license-info) in effect on the date of 55 publication of this document. Please review these documents 56 carefully, as they describe your rights and restrictions with respect 57 to this document. Code Components extracted from this document must 58 include Simplified BSD License text as described in Section 4.e of 59 the Trust Legal Provisions and are provided without warranty as 60 described in the Simplified BSD License. 62 Table of Contents 64 1. Terminologies . . . . . . . . . . . . . . . . . . . . . . . . 2 65 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 66 2.1. MVPN RPT-SPT Mode . . . . . . . . . . . . . . . . . . . . 4 67 3. Specification . . . . . . . . . . . . . . . . . . . . . . . . 4 68 4. Security Considerations . . . . . . . . . . . . . . . . . . . 5 69 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 70 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 71 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 72 7.1. Normative References . . . . . . . . . . . . . . . . . . 6 73 7.2. Informative References . . . . . . . . . . . . . . . . . 6 74 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6 76 1. Terminologies 78 Familiarity with MVPN and MSDP protocols and procedures is assumed. 79 Some terminologies are listed below for convenience. 81 o ASM: Any source multicast. 83 o SPT: Source-specific Shortest-path Tree. 85 o C-S: A multicast source address, identifying a multicast source 86 located at a VPN customer site. 88 o C-G: A multicast group address used by a VPN customer. 90 o C-RP: A multicast Rendezvous Point for a VPN customer. 92 o EC: Extended Community. 94 2. Introduction 96 Section "14. Supporting PIM-SM without Inter-Site Shared C-Trees" of 97 [RFC6514] specifies the procedures for MVPN PEs to discover (C-S,C-G) 98 via MVPN Source Active A-D routes and then send (C-S,C-G) C-multicast 99 routes towards the ingress PEs, to establish SPTs for customer ASM 100 flows for which they have downstream receivers. (C-*,C-G) 101 C-multicast routes are not sent among the PEs so inter-site shared 102 C-Trees are not used and the method is generally referred to as "spt- 103 only" mode. 105 With this mode, the MVPN Source Active routes are functionally 106 similar to MSDP Source-Active messages [RFC3618]. One or more of the 107 PEs, say PE1, either act as a C-RP and learn of (C-S,C-G) via PIM 108 Register messages, or have MSDP sessions with some MSDP peers and 109 learn (C-S,C-G) via MSDP SA messages. In either case, PE1 will then 110 originate MVPN SA routes for other PEs to learn the (C-S,C-G). 112 [RFC6514] only specifies that a PE receiving the MVPN SA routes, say 113 PE2, will advertise (C-S,C-G) C-multicast routes if it has 114 corresponding (C-*,C-G) state learnt from its CE. PE2 may also have 115 MSDP sessions with other C-RPs at its site, but [RFC6514] does not 116 specify that it advertises MSDP SA messages to those MSDP peers for 117 the (C-S,C-G) that it learns via MVPN SA routes. PE2 would need to 118 have an MSDP session with PE1 (that advertised the MVPN SA messages) 119 to learn the sources via MSDP SA messages, for it to advertise the 120 MSDP SA to its local peers. To make things worse, unless blocked by 121 policy control, PE2 would in turn advertise MVPN SA routes because of 122 those MSDP SA messages that it receives from PE1, which are redundant 123 and unnecessary. Also notice that the PE1-PE2 MSDP session is VPN- 124 specific, while the BGP sessions over which the MVPN routes are 125 advertised are not. 127 If a PE does advertise MSDP SA messages based on received MVPN SA 128 routes, the VPN-specific MSDP sessions are no longer needed. 129 Additionally, this MVPN/MSDP SA interoperation has the following 130 inherent benefits for a BGP based solution. 132 o MSDP SA refreshes are replaced with BGP hard state. 134 o Route Reflectors can be used instead of having peer-to-peer 135 sessions. 137 o VPN extranet mechanisms can be used to propagate (C-S,C-G) 138 information across VPNs with flexible policy control. 140 While MSDP Source Active routes contain the source, group and RP 141 addresses of a given multicast flow, MVPN Source Active routes only 142 contain the source and group. MSDP requires the RP address 143 information in order to perform peer-RPF. Therefore, this document 144 describes how to convey the RP address information into the MVPN 145 Source Active route using an Extended Community so this information 146 can be shared with an existing MSDP infrastructure. 148 The procedures apply to Global Table Multicast (GTM) [RFC7716] as 149 well. 151 2.1. MVPN RPT-SPT Mode 153 For comparison, another method of supporting customer ASM is 154 generally referred to as "rpt-spt" mode. Section "13. Switching 155 from a Shared C-Tree to a Source C-Tree" of [RFC6514] specifies the 156 MVPN SA procedures for that mode, but those SA routes are a 157 replacement for PIM-ASM assert and (s,g,rpt) prune mechanisms, not 158 for source discovery purposes. MVPN/MSDP SA interoperation for the 159 "rpt-spt" mode is outside of the scope of this document. In the rest 160 of the document, the "spt-only" mode is assumed. 162 3. Specification 164 The MVPN PEs that act as customer RPs or have one or more MSDP 165 sessions in a VPN (or the global table in case of GTM) are treated as 166 an MSDP mesh group for that VPN (or the global table). In the rest 167 of the document, it is referred to as the PE mesh group. It MUST NOT 168 include other MSDP speakers, and is integrated into the rest of MSDP 169 infrastructure for the VPN (or the global table) following normal 170 MSDP rules and practices. 172 When an MVPN PE advertises an MVPN SA route following procedures in 173 [RFC6514] for the "spt-only" mode, it SHOULD attach an "MVPN SA RP- 174 address Extended Community". This is a Transitive IPv4-Address- 175 Specific Extended Community. The Local Administrative field is set 176 to zero and the Global Administrative field is set to an RP address 177 determined as the following: 179 o If the (C-S,C-G) is learnt as result of PIM Register mechanism, 180 the local RP address for the C-G is used. 182 o If the (C-S,C-G) is learnt as result of incoming MSDP SA messages, 183 the RP address in the selected MSDP SA message is used. 185 In addition to procedures in [RFC6514], an MVPN PE may be provisioned 186 to generate MSDP SA messages from received MVPN SA routes, with or 187 without fine grained policy control. If a received MVPN SA route is 188 to trigger MSDP SA message, it is treated as if a corresponding MSDP 189 SA message was received from within the PE mesh group and normal MSDP 190 procedure is followed (e.g. an MSDP SA message is advertised to other 191 MSDP peers outside the PE mesh group). The (S,G) information comes 192 from the (C-S,C-G) encoding in the MVPN SA NLRI and the RP address 193 comes from the "MVPN SA RP-address EC" mentioned above. If the 194 received MVPN SA route does not have the EC (this could be from a 195 legacy PE that does not have the capability to attach the EC), the 196 local RP address for the C-G is used. In that case, it is possible 197 that receiving PE's RP for the C-G is actually the MSDP peer to which 198 the generated MSDP message is advertised, causing the peer to discard 199 it due to RPF failure. To get around that problem the peer SHOULD 200 use local policy to accept the MSDP SA message. 202 An MVPN PE MAY treat only the best MVPN SA route selected by BGP 203 route selection process (instead of all MVPN SA routes) for a given 204 (C-S,C-G) as a received MSDP SA message (and advertise corresponding 205 MSDP message). In that case, if the selected best MVPN SA route does 206 not have the "MVPN SA RP-address EC" but another route for the same 207 (C-S, C-G) does, then the best route with the EC SHOULD be chosen. 208 As a result, when/if the best MVPN SA route with the EC changes, a 209 new MSDP SA message is advertised if the RP address determined 210 according to the newly selected MVPN SA route is different from 211 before. The previously advertised MSDP SA message with the older RP 212 address will be timed out. 214 4. Security Considerations 216 RFC6514 specifies the procedure for a PE to generate an MVPN SA upon 217 discovering a (C-S,C-G) flow (e.g. via a received MSDP SA message) in 218 a VPN. This document extends this capability in the reverse 219 direction - upon receiving an MVPN SA route in a VPN generate 220 corresponding MSDP SA and advertise to MSDP peers in the same VPN. 221 As such, the capabilities specified in this document introduce no 222 additional security considerations beyond those already specified in 223 RFC6514 and RFC3618. Moreover, the capabilities specified in this 224 document actually eliminate the control message amplification that 225 exists today where VPN-specific MSDP sessions are required among the 226 PEs that are customer MSDP peers, which lead to redundant messages 227 (MSDP SAs and MVPN SAs) being carried in parallel between PEs. 229 5. IANA Considerations 231 This document introduces a new Transitive IPv4 Address Specific 232 Extended Community "MVPN SA RP-address Extended Community". IANA has 233 registered subcode 0x20 in the Transitive IPv4-Address-Specific 234 Extended Community Sub-Types registry for this EC. 236 6. Acknowledgements 238 The authors thank Eric Rosen and Vinod Kumar for their review, 239 comments, questions and suggestions for this document. The authors 240 also thank Yajun Liu for her review and comments. 242 7. References 244 7.1. Normative References 246 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 247 Requirement Levels", BCP 14, RFC 2119, 248 DOI 10.17487/RFC2119, March 1997, 249 . 251 [RFC6514] Aggarwal, R., Rosen, E., Morin, T., and Y. Rekhter, "BGP 252 Encodings and Procedures for Multicast in MPLS/BGP IP 253 VPNs", RFC 6514, DOI 10.17487/RFC6514, February 2012, 254 . 256 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 257 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 258 May 2017, . 260 7.2. Informative References 262 [RFC3618] Fenner, B., Ed. and D. Meyer, Ed., "Multicast Source 263 Discovery Protocol (MSDP)", RFC 3618, 264 DOI 10.17487/RFC3618, October 2003, 265 . 267 [RFC7716] Zhang, J., Giuliano, L., Rosen, E., Ed., Subramanian, K., 268 and D. Pacella, "Global Table Multicast with BGP Multicast 269 VPN (BGP-MVPN) Procedures", RFC 7716, 270 DOI 10.17487/RFC7716, December 2015, 271 . 273 Authors' Addresses 275 Zhaohui Zhang 276 Juniper Networks 278 EMail: zzhang@juniper.net 279 Lenny Giuliano 280 Juniper Networks 282 EMail: lenny@juniper.net