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'PIMAUTH' ** Obsolete normative reference: RFC 1825 (Obsoleted by RFC 2401) ** Downref: Normative reference to an Historic RFC: RFC 1828 ** Obsolete normative reference: RFC 2362 (Obsoleted by RFC 4601, RFC 5059) ** Downref: Normative reference to an Informational RFC: RFC 2382 ** Obsolete normative reference: RFC 2385 (Obsoleted by RFC 5925) Summary: 14 errors (**), 0 flaws (~~), 8 warnings (==), 5 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 MBONED Working Group Dorian Kim 2 Internet Draft Verio 3 David Meyer 4 Cisco Systems 5 Henry Kilmer 6 Dino Farinacci 8 Category Informational 9 November, 1999 11 Anycast RP mechanism using PIM and MSDP 12 14 1. Status of this Memo 16 This document is an Internet-Draft and is in full conformance with 17 all provisions of Section 10 of RFC2026. 19 2026 are working documents of the Internet Engineering Task Force 20 (IETF), its areas, and its working groups. Note that other groups 21 may also distribute working documents as Internet- Drafts. 23 Internet-Drafts are draft documents valid for a maximum of six months 24 and may be updated, replaced, or obsoleted by other documents at any 25 time. It is inappropriate to use Internet- Drafts as reference 26 material or to cite them other than as "work in progress." 28 The list of current Internet-Drafts can be accessed at 29 http://www.ietf.org/ietf/1id-abstracts.txt. 31 The list of Internet-Draft Shadow Directories can be accessed at 32 http://www.ietf.org/shadow.html. 34 2. Abstract 36 This document describes a mechanism to allow for an arbitrary number 37 of RPs per group in a single share-tree PIM-SM domain. 39 This memo is a product of the MBONE Deployment Working Group (MBONED) 40 in the Operations and Management Area of the Internet Engineering 41 Task Force. Submit comments to or the 42 authors. 44 3. Copyright Notice 46 Copyright (C) The Internet Society (1999). All Rights Reserved. 48 4. Introduction 50 PIM-SM as currently defined allows for only a single active RP per 51 group, and as such the decision of optimal RP placement can become 52 problematic for a multi-regional network deploying PIM-SM. 54 The single active RP, or flat RP space design of PIM-SM has several 55 implications, including traffic concentration, lack of scalable load 56 balancing and redundancy between RPs, sub-optimal forwarding of 57 multicast packets, and distant RP dependencies. These properties of 58 PIM-SM have been demonstrated in recent native continental or inter- 59 continental scale multicast deployments. As a result, it became clear 60 that ISP backbones require a mechanism that allows definition of 61 multiple active RPs per group in single PIM-SM domain. Further, any 62 such mechanism should also addresses the issues addressed above. 64 The mechanism described here is intended to address the need for 65 redundancy and load sharing among RPs in a domain. It is primarily 66 intended for application within those networks which are using MBGP, 67 MSDP and PIM-SM protocols for native multicast deployment, although 68 it not limited to those protocols. In particular, Anycast RP is 69 applicable in any PIM-SM network that also supports MSDP (MSDP is 70 required so that the various RPs in the domain maintain a consistent 71 view of the sources that are active). Note however, a domain 72 deploying Anycast RP is not required to run MBGP. 74 5. Problem Definition 76 The anycast RP solution provides a solution for both redundancy and 77 load balancing among any number of active RPs in a domain. 79 5.1. Traffic Concentration and Load Balancing Between RPs 81 While PIM-SM allows for multiple RPs to be defined for a given group, 82 only one group to RP mapping can active at a given time. A 83 traditional deployment mechanism for load balancing between multiple 84 RPs covering the multicast group space is to split up the 224.0.0.0/4 85 space between multiple defined RPs. This is an acceptable solution as 86 long as multicast traffic remains low, but has problems as multicast 87 traffic increases, especially because the network operator defining 88 group space split between RPs does not alway have a priori knowledge 89 of traffic distribution between groups. This can be overcome via 90 periodic reconfigurations, but operational considerations cause this 91 type of solution to scale poorly. The other alternative to periodic 92 reconfiguration is to split 224.0.0.0/4 space more finely between 93 more RPs, but this solution can have the disadvantage of creating 94 more complex RP configurations, along with the attendant operational 95 problems when RPs are configured [CLUSTERS]. 97 5.2. Sub-optimal Forwarding of Multicast Packets 99 When a single RP serves a given multicast group, all joins to that 100 group will be sent to that RP regardless of the topological distance 101 between the RP and the sources and receivers. Initial data will be 102 sent towards the RP also until configured shortest path tree switch 103 threshold is is reached, or the data will always be sent towards the 104 RP if the network is configured to always use RP rooted shared tree. 105 This holds true even if all the sources and the receivers are in any 106 given single region, and RP is topologically distant from the sources 107 and the receivers. This is an artifact of the dynamic nature of 108 multicast group members, and of the fact that operators may not 109 always have a priori knowledge of the topological placement of the 110 group members. 112 Taken together, these effects can mean that (for example) although 113 all the sources and receivers of a given group are in Europe, they 114 are joining towards the RP in USA and the data will be traversing 115 relatively expensive pipe(s) twice, once to get to RP, and back down 116 the RP rooted tree again, creating inefficient use of expensive 117 resources. 119 5.3. Distant RP Dependencies 121 As outlined above, single active RP per group may cause local sources 122 and receivers to become dependent on a topologically distant RP. In 123 case of a scenario where there are backup RPs configured, distant RP 124 dependence can be created due to the failure of the primary RP, which 125 is topologically closer, and may become exacerbated by switching to 126 the backup RP, which may be even more distant topologically, which 127 may lead to inferior performance, if not outright loss of 128 connectivity to an RP serving the group, depending on the network 129 condition at the given moment. 131 6. Solution 133 Given the problem set outlined above, a good solution would allow an 134 operator to define multiple RPs per group, and distribute those RPs 135 in a topologically significant manner to the sources and receivers. 137 6.1. Mechanisms 139 All the RPs serving a given group or set of groups are configured 140 with identical unicast address, using a numbered interface on the RPs 141 (frequently a logical interface such as a loopback is used). RPs then 142 advertise group to RP mappings using this interface address. This 143 will cause group members (senders) to join (register) towards the 144 topologically closest RP. RPs MSDP peer with each other using the 145 unique shared addresses. Note that if the router implementation 146 chooses the shared address for the BGP router ID, then BGP peerings 147 will not be established. As a result, care should be taken to avoid 148 the ambiguity of the BGP router ID with the RP address (for example, 149 if the logical address chosen is the highest IP address configured on 150 the router, and the router implementation that automatically chooses 151 a router ID based upon highest IP address assigned to interfaces). 152 Finally, the solution described here can be implemented without any 153 modification to existing protocols or their implementations. 155 6.2. Interaction with MSDP Peer-RPF check 157 Each MSDP peer receives and forwards the message away from the RP 158 address in a "peer-RPF flooding" fashion. The notion of peer-RPF 159 flooding is with respect to forwarding SA messages [MSDP]. The BGP or 160 MBGP routing tables are examined to determine which peer is the next 161 hop towards the originating RP of the SA message. Such a peer is 162 called an "RPF peer". See [MSDP] for details of the Peer-RPF check. 164 6.3. Further Applications of Anycast RP mechanism 166 The solution described above can also be applied to external MSDP 167 peers that are used to join two PIM-SM domains together. This can 168 provide redundancy to the MSDP peering session, ease operational 169 complexity as well as simplify configuration management. A side 170 effect to be aware of with this design is that which of the 171 configured MSDP sessions comes up will be determined via the unicast 172 topology between two providers, and can be some what unpredictable. 173 If any of the backup peering sessions resets, the active session will 174 also reset. 176 7. Multicast State Scaling 178 Let k = m + r, where 180 r = registering to an RP 181 m = number internal sources learned through MSDP 182 p = number of anycast (internal) MSDP peers 184 For p = 1, m = 0 186 0 receivers ==> 1 (*,G) + 0 SAs 187 Greater than 1 receiver ==> k (S,G) + 0 SAs 189 For p > 1, m != 0 191 0 receivers ==> 1 (*,G) + m SAs 192 Greater than 1 receiver ==> k (S,G) + m SAs 194 Importantly, the multicast state growth is O(k), where k is not a 195 function of p, the number of anycast RP peers. 197 8. Security considerations 199 Since the solution described here makes heavy use of anycast 200 addressing, care must be taken to avoid spoofing. In particular 201 unicast routing and PIM RPs must be protected. 203 8.1. Unicast Routing 205 Both internal and external unicast routing can be weakly protected 206 with keyed MD5 [RFC1828], as implemented in an internal protocol such 207 as OSPF [RFC2382] or in BGP [RFC2385]. More generally, IPSEC 208 [RFC1825] could be used to provide protocol integrity for the unicast 209 routing system. 211 8.2. Multicast Protocol Integrity 213 The mechanisms described in [PIMAUTH] should be used to provide 214 protocol message integrity protection and group-wise message origin 215 authentication. 217 8.3. MSDP Peer Integrity 219 As is the the case for BGP, MSDP peers can be protected using keyed 220 MD5 [RFC1828]. 222 9. Acknowledgments 224 John Meylor, Dave Thaler and Tom Pusateri provided insightful 225 comments on earlier versions for this idea. 227 10. References 229 [CLUSTERS] D. Farinacci, et. al., "Use of Anycast Clusters for 230 Inter-Domain Multicast Routing", 231 draft-ietf-farinacci-anycast-clusters-01.txt, March, 232 1998. ftp://ftpeng.cisco.com/ipmulticast/internet-drafts 234 [MSDP] D. Farinacci, et. al., "Multicast Source Discovery 235 Protocol (MSDP)", draft-ietf-msdp-spec-02.txt, 236 November, 1999. 238 [PIMAUTH] L. Wei, et al., "Authenticating PIM version 2 messages", 239 draft-ietf-pim-v2-auth-00.txt, November, 1998. 241 [RFC1825] Atkinson, R., "IP Security Architecture", August 1995. 243 [RFC1828] P. Metzger and W. Simpson, "IP Authentication using Keyed 244 MD5", RFC 1828, August, 1995. 246 [RFC2362] D. Estrin, et. al., "Protocol Independent Multicast- 247 Sparse Mode (PIM-SM): Protocol Specification", RFC 248 2362, June, 1998. 250 [RFC2382] Moy, J., "OSPF Version 2", RFC 2382, April 1998. 252 [RFC2385] Herrernan, A., "Protection of BGP Sessions via the TCP 253 MD5 Signature Option", RFC 2385, August, 1998. 255 [RFC2403] C. Madson and R. Glenn, "The Use of HMAC-MD5-96 within 256 ESP and AH", RFC 2403, November, 1998. 258 11. Author's Address 260 Dorian Kim 261 Verio, Inc. 262 2361 Lancashire Dr. #2A 263 Ann Arbor, MI 48015 264 Email: dorian@blackrose.org 266 Hank Kilmer 267 Email: hank@rem.com 269 Dino Farinacci 270 Email: dino@dinof.net 272 David Meyer 273 Cisco Systems, Inc. 274 170 Tasman Drive 275 San Jose, CA, 95134 276 Email: dmm@cisco.com