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Please use uppercase 'NOT' together with RFC 2119 keywords (if that is what you mean). Found 'MUST not' in this paragraph: First a PIM Hello MUST be sent with priority 0. Once it has gotten Hello from other PIM neighbors, it knows that it is not eligible to be PIM DR or BDR. It MUST send configured PIM DR priority immediately. It MUST not wait for next hello interval. -- The document date (October 23, 2019) is 1645 days in the past. Is this intentional? Checking references for intended status: Informational ---------------------------------------------------------------------------- == Outdated reference: A later version (-14) exists of draft-ietf-pim-dr-improvement-04 ** Obsolete normative reference: RFC 4601 (Obsoleted by RFC 7761) Summary: 1 error (**), 0 flaws (~~), 3 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group M. Mishra 3 Internet-Draft J. Goh 4 Intended status: Informational Cisco Systems 5 Expires: April 25, 2020 G. Mishra 6 Verizon Communications Inc. (VZ) 7 October 23, 2019 9 PIM Backup Designated Router Procedure 10 draft-mankamana-pim-bdr-03 12 Abstract 14 On a multi-access network, one of the PIM routers is elected as a 15 Designated Router (DR). On the last hop LAN, the PIM DR is 16 responsible for tracking local multicast listeners and forwarding 17 traffic to these listeners if the group is operating in PIM-SM. In 18 this document, we propose a mechanism to elect backup DR on a shared 19 LAN. A backup DR on LAN would be useful for faster convergence. 20 This draft introduces the concept of a Backup Designated Router (BDR) 21 and the procedure to implement it. 23 Status of This Memo 25 This Internet-Draft is submitted in full conformance with the 26 provisions of BCP 78 and BCP 79. 28 Internet-Drafts are working documents of the Internet Engineering 29 Task Force (IETF). Note that other groups may also distribute 30 working documents as Internet-Drafts. The list of current Internet- 31 Drafts is at https://datatracker.ietf.org/drafts/current/. 33 Internet-Drafts are draft documents valid for a maximum of six months 34 and may be updated, replaced, or obsoleted by other documents at any 35 time. It is inappropriate to use Internet-Drafts as reference 36 material or to cite them other than as "work in progress." 38 This Internet-Draft will expire on April 25, 2020. 40 Copyright Notice 42 Copyright (c) 2019 IETF Trust and the persons identified as the 43 document authors. All rights reserved. 45 This document is subject to BCP 78 and the IETF Trust's Legal 46 Provisions Relating to IETF Documents 47 (https://trustee.ietf.org/license-info) in effect on the date of 48 publication of this document. Please review these documents 49 carefully, as they describe your rights and restrictions with respect 50 to this document. Code Components extracted from this document must 51 include Simplified BSD License text as described in Section 4.e of 52 the Trust Legal Provisions and are provided without warranty as 53 described in the Simplified BSD License. 55 Table of Contents 57 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 58 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 59 3. Applicability and deviation from draft PIM DR Improvement . . 4 60 4. Protocol Specification . . . . . . . . . . . . . . . . . . . 4 61 4.1. PIM Backup DR (BDR) election procedure . . . . . . . . . 4 62 4.2. Existing PIM DR failure . . . . . . . . . . . . . . . . . 4 63 4.3. Existing PIM BDR failure . . . . . . . . . . . . . . . . 4 64 4.4. New PIM Router addition in network . . . . . . . . . . . 4 65 4.4.1. New PIM router eligible to be PIM DR on shared LAN . 4 66 4.4.2. New PIM router eligible to be PIM BDR on shared LAN . 5 67 4.4.3. New PIM router is not eligible to be PIM DR or BDR on 68 shared LAN . . . . . . . . . . . . . . . . . . . . . 5 69 4.5. Initial case, All new PIM router coming up in shared LAN 5 70 4.6. Benefit . . . . . . . . . . . . . . . . . . . . . . . . . 6 71 5. Compatibility . . . . . . . . . . . . . . . . . . . . . . . . 6 72 6. Manageability Considerations . . . . . . . . . . . . . . . . 6 73 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 74 8. Security Considerations . . . . . . . . . . . . . . . . . . . 6 75 9. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 6 76 10. Normative References . . . . . . . . . . . . . . . . . . . . 6 77 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 79 1. Introduction 81 On a multi-access LAN such as an Ethernet, one of the PIM routers is 82 elected as a DR. The PIM DR has two roles in the PIM-SM protocol. 83 On the first hop network, the PIM DR is responsible for registering 84 an active source with the Rendezvous Point (RP) if the group is 85 operating in PIM-SM. On the last hop LAN, the PIM DR is responsible 86 for tracking local multicast listeners and forwarding to these 87 listeners if the group is operating in PIM-SM. 89 Consider the following last hop LAN in Figure 1: 91 ( core networks ) 92 | | | 93 | | | 94 R1 R2 R3 95 | | | 96 --(last hop LAN)-- 97 | 98 | 99 (many receivers) 101 Figure 1: Last Hop LAN 103 Assume R1 is elected as the Designated Router. According to 104 [RFC4601], R1 will be responsible for forwarding traffic to that LAN 105 on behalf of any local member. In addition to keeping track of IGMP 106 and MLD membership reports, R1 is also responsible for initiating the 107 creation of source and/or shared trees towards the senders or the 108 RPs. 110 There are multiple reasons for why network could potentially trigger 111 DR re-election. Some of the reasons are 113 1. R1 going down 115 2. Access interface towards shared LAN going down 117 3. Config changed with lower DR priority 119 When any of above network event occurs, PIM DR re-election would be 120 triggered. When a new DR is elected in shared LAN, new DR would be 121 responsible to build a multicast tree towards source / RP. There are 122 some cases, where traffic is crucial and the operator wants to have 123 minimum traffic loss with DR failure. To address this requirement, 124 this draft introduces a backup DR election procedure which would 125 minimize traffic loss during PIM DR failure. 127 2. Terminology 129 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 130 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 131 document are to be interpreted as described in [RFC2119] . 133 BDR - PIM Backup DR 135 With respect to PIM, this document follows the terminology that has 136 been defined in [RFC4601] . 138 3. Applicability and deviation from draft PIM DR Improvement 140 [I-D.ietf-pim-dr-improvement] defines procedure to solve same problem 141 which was stated in the introduction section of this draft. 142 [I-D.ietf-pim-dr-improvement] introduces new PIM Hello options for 143 election of backup PIM DR. 145 This draft provides mechanism to elect BDR without using any new PIM 146 Hello. 148 4. Protocol Specification 150 4.1. PIM Backup DR (BDR) election procedure 152 [RFC7761] defines procedure for PIM DR election. PIM DR is elected 153 on interface "I" among all PIM routers for which "I" has received PIM 154 Hello. BDR election follows the exact same procedure and the second 155 best PIM DR on shared LAN to be chosen as BDR on interface "I" 157 BDR would perform each of the responsibility of PIM DR except it 158 would not forward traffic on shared LAN. 160 4.2. Existing PIM DR failure 162 When PIM DR fails, PIM DR re-election is triggered on shared LAN. 163 Since BDR is second best DR in LAN, it MUST take over immediately and 164 MUST start forwarding multicast traffic on shared LAN. 166 Again on a shared LAN, new BDR would be elected. and current BDR 167 would be the new DR. 169 4.3. Existing PIM BDR failure 171 When an existing PIM BDR fails, the shared LAN MUST have BDR re- 172 election using the DR election procedure from [RFC7761]. 174 4.4. New PIM Router addition in network 176 When a new PIM router is added in shared LAN, It could be either one 177 of the below defined roles. 179 4.4.1. New PIM router eligible to be PIM DR on shared LAN 181 When a new PIM router is added in a shared LAN and has the highest 182 PIM DR priority configured, if a new router starts propagating its 183 configured DR priority right away, the existing PIM DR would give up 184 its role. Then there would be potential traffic loss till the new DR 185 learns about membership states and builds a multicast tree to the 186 source or RP. 188 To avoid any such traffic loss situation, new PIM router SHOULD send 189 a PIM Hello with priority 0. After 2 (default value, SHOULD have way 190 to configure) PIM Hello interval or IGMP Query Interval (Which ever 191 is higher) it SHOULD start propagating its original configured DR 192 priority. 194 Even though a new PIM router propagating its priority as 0, it MUST 195 start building a multicast tree towards source / RP, This is So that 196 traffic loss could be minimized once it starts sending Hello with 197 configured DR priority. 199 For a brief amount of time, there would be multiple copies of flows 200 present in the multicast core, but a user SHOULD be able to configure 201 whether to send hello with 0 priority or a configured priority. 202 Depending on the application tolerance (Traffic loss Vs Extra traffic 203 in core) the operator can choose option whichever is suitable for 204 network. 206 After a PIM Hello or IGMP Query interval, the network would get 207 stable with only one DR and one BDR. 209 4.4.2. New PIM router eligible to be PIM BDR on shared LAN 211 It SHOULD follow the exact same procedure defined in the previous 212 section. 214 4.4.3. New PIM router is not eligible to be PIM DR or BDR on shared LAN 216 First a PIM Hello MUST be sent with priority 0. Once it has gotten 217 Hello from other PIM neighbors, it knows that it is not eligible to 218 be PIM DR or BDR. It MUST send configured PIM DR priority 219 immediately. It MUST not wait for next hello interval. 221 4.5. Initial case, All new PIM router coming up in shared LAN 223 In this case, initially each of the PIM routers would send Hellos 224 with priorities of 0. If a PIM router receives all Hellos with 225 priorities 0, it MUST send out a Hello with a configured PIM DR 226 priority. Since it is initial startup case, it would take up to one 227 Hello interval to converge. 229 4.6. Benefit 231 1. Easy to implement as it uses an existing PIM procedure to elect 232 DR. 234 2. Does not introduce any new Hello option 236 5. Compatibility 238 6. Manageability Considerations 240 7. IANA Considerations 242 8. Security Considerations 244 9. Acknowledgement 246 The author would like to thank Stig Venaas, Tharak Abraham, Anish 247 Kachinthaya, Anvitha Kachinthaya for helping with original idea. 249 10. Normative References 251 [I-D.ietf-pim-dr-improvement] 252 Zhang, Z., hu, f., Xu, B., and m. mishra, "PIM DR 253 Improvement", draft-ietf-pim-dr-improvement-04 (work in 254 progress), December 2017. 256 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 257 Requirement Levels", BCP 14, RFC 2119, 258 DOI 10.17487/RFC2119, March 1997, 259 . 261 [RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas, 262 "Protocol Independent Multicast - Sparse Mode (PIM-SM): 263 Protocol Specification (Revised)", RFC 4601, 264 DOI 10.17487/RFC4601, August 2006, 265 . 267 [RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., 268 Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent 269 Multicast - Sparse Mode (PIM-SM): Protocol Specification 270 (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March 271 2016, . 273 Authors' Addresses 275 Mankamana Mishra 276 Cisco Systems 277 821 Alder Drive, 278 MILPITAS, CALIFORNIA 95035 279 UNITED STATES 281 Email: mankamis@cisco.com 283 Joseph Goh 284 Cisco Systems 285 SINGAPORE 287 Email: hocgoh@cisco.com 289 Gyan S. Mishra 290 Verizon Communications Inc. (VZ) 291 13101 Columbia Pike FDC1 Rm 304-D 292 Silver Spring MD 20904 293 UNITED STATES 295 Email: gyan.s.mishra@verizon.com