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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 22, 2018) is 2012 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for intended status: Informational ---------------------------------------------------------------------------- == Outdated reference: A later version (-14) exists of draft-ietf-pim-dr-improvement-04 ** Obsolete normative reference: RFC 4601 (Obsoleted by RFC 7761) Summary: 1 error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 Mankamana. Mishra 3 Internet-Draft Cisco Systems 4 Intended status: Informational October 22, 2018 5 Expires: April 25, 2019 7 PIM Backup Designated Router Procedure 8 draft-mankamana-pim-bdr-01 10 Abstract 12 On a multi-access network, one of the PIM routers is elected as a 13 Designated Router (DR). On the last hop LAN, the PIM DR is 14 responsible for tracking local multicast listeners and forwarding 15 traffic to these listeners if the group is operating in PIM-SM. In 16 this document, we propose a mechanism to elect backup DR on a shared 17 LAN. A backup DR on LAN would be useful for faster convergence. 18 This draft introduces the concept of a Backup Designated Router (BDR) 19 and the procedure to implement it. 21 Status of This Memo 23 This Internet-Draft is submitted in full conformance with the 24 provisions of BCP 78 and BCP 79. 26 Internet-Drafts are working documents of the Internet Engineering 27 Task Force (IETF). Note that other groups may also distribute 28 working documents as Internet-Drafts. The list of current Internet- 29 Drafts is at https://datatracker.ietf.org/drafts/current/. 31 Internet-Drafts are draft documents valid for a maximum of six months 32 and may be updated, replaced, or obsoleted by other documents at any 33 time. It is inappropriate to use Internet-Drafts as reference 34 material or to cite them other than as "work in progress." 36 This Internet-Draft will expire on April 25, 2019. 38 Copyright Notice 40 Copyright (c) 2018 IETF Trust and the persons identified as the 41 document authors. All rights reserved. 43 This document is subject to BCP 78 and the IETF Trust's Legal 44 Provisions Relating to IETF Documents 45 (https://trustee.ietf.org/license-info) in effect on the date of 46 publication of this document. Please review these documents 47 carefully, as they describe your rights and restrictions with respect 48 to this document. Code Components extracted from this document must 49 include Simplified BSD License text as described in Section 4.e of 50 the Trust Legal Provisions and are provided without warranty as 51 described in the Simplified BSD License. 53 Table of Contents 55 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 56 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 57 3. Applicability and deviation from draft PIM DR Improvement . . 4 58 4. Protocol Specification . . . . . . . . . . . . . . . . . . . 4 59 4.1. PIM Backup DR (BDR) election procedure . . . . . . . . . 4 60 4.2. Existing PIM DR failure . . . . . . . . . . . . . . . . . 4 61 4.3. Existing PIM BDR failure . . . . . . . . . . . . . . . . 4 62 4.4. New PIM Router addition in network . . . . . . . . . . . 4 63 4.4.1. New PIM router eligible to be PIM DR on shared LAN . 4 64 4.4.2. New PIM router eligible to be PIM BDR on shared LAN . 5 65 4.4.3. New PIM router is not eligible to be PIM DR or BDR on 66 shared LAN . . . . . . . . . . . . . . . . . . . . . 5 67 4.5. Initial case, All new PIM router coming up in shared LAN 5 68 4.6. Benefit . . . . . . . . . . . . . . . . . . . . . . . . . 6 69 5. Compatibility . . . . . . . . . . . . . . . . . . . . . . . . 6 70 6. Manageability Considerations . . . . . . . . . . . . . . . . 6 71 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 72 8. Security Considerations . . . . . . . . . . . . . . . . . . . 6 73 9. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 6 74 10. Normative References . . . . . . . . . . . . . . . . . . . . 6 75 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7 77 1. Introduction 79 On a multi-access LAN such as an Ethernet, one of the PIM routers is 80 elected as a DR. The PIM DR has two roles in the PIM-SM protocol. 81 On the first hop network, the PIM DR is responsible for registering 82 an active source with the Rendezvous Point (RP) if the group is 83 operating in PIM-SM. On the last hop LAN, the PIM DR is responsible 84 for tracking local multicast listeners and forwarding to these 85 listeners if the group is operating in PIM-SM. 87 Consider the following last hop LAN in Figure 1: 89 ( core networks ) 90 | | | 91 | | | 92 R1 R2 R3 93 | | | 94 --(last hop LAN)-- 95 | 96 | 97 (many receivers) 99 Figure 1: Last Hop LAN 101 Assume R1 is elected as the Designated Router. According to 102 [RFC4601], R1 will be responsible for forwarding traffic to that LAN 103 on behalf of any local member. In addition to keeping track of IGMP 104 and MLD membership reports, R1 is also responsible for initiating the 105 creation of source and/or shared trees towards the senders or the 106 RPs. 108 There are multiple reasons for why network could potentially trigger 109 DR re-election. Some of the reasons are 111 1. R1 going down 113 2. Access interface towards shared LAN going down 115 3. Config changed with lower DR priority 117 When any of above network event occurs, PIM DR re-election would be 118 triggered. When a new DR is elected in shared LAN, new DR would be 119 responsible to build a multicast tree towards source / RP. There are 120 some cases, where traffic is crucial and the operator wants to have 121 minimum traffic loss with DR failure. To address this requirement, 122 this draft introduces a backup DR election procedure which would 123 minimize traffic loss during PIM DR failure. 125 2. Terminology 127 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 128 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 129 document are to be interpreted as described in [RFC2119] . 131 BDR - PIM Backup DR 133 With respect to PIM, this document follows the terminology that has 134 been defined in [RFC4601] . 136 3. Applicability and deviation from draft PIM DR Improvement 138 [I-D.ietf-pim-dr-improvement] defines procedure to solve same problem 139 which was stated in the introduction section of this draft. 140 [I-D.ietf-pim-dr-improvement] introduces new PIM Hello options for 141 election of backup PIM DR. 143 This draft provides mechanism to elect BDR without using any new PIM 144 Hello. 146 4. Protocol Specification 148 4.1. PIM Backup DR (BDR) election procedure 150 [RFC7761] defines procedure for PIM DR election. PIM DR is elected 151 on interface "I" among all PIM routers for which "I" has received PIM 152 Hello. BDR election follows the exact same procedure and the second 153 best PIM DR on shared LAN to be chosen as BDR on interface "I" 155 BDR would perform each of the responsibility of PIM DR except it 156 would not forward traffic on shared LAN. 158 4.2. Existing PIM DR failure 160 When PIM DR fails, PIM DR re-election is triggered on shared LAN. 161 Since BDR is second best DR in LAN, it MUST take over immediately and 162 MUST start forwarding multicast traffic on shared LAN. 164 Again on a shared LAN, new BDR would be elected. and current BDR 165 would be the new DR. 167 4.3. Existing PIM BDR failure 169 When an existing PIM BDR fails, the shared LAN MUST have BDR re- 170 election using the DR election procedure from [RFC7761]. 172 4.4. New PIM Router addition in network 174 When a new PIM router is added in shared LAN, It could be either one 175 of the below defined roles. 177 4.4.1. New PIM router eligible to be PIM DR on shared LAN 179 When a new PIM router is added in a shared LAN and has the highest 180 PIM DR priority configured, if a new router starts propagating its 181 configured DR priority right away, the existing PIM DR would give up 182 its role. Then there would be potential traffic loss till the new DR 183 learns about membership states and builds a multicast tree to the 184 source or RP. 186 To avoid any such traffic loss situation, new PIM router SHOULD send 187 a PIM Hello with priority 0. After 2 (default value, SHOULD have way 188 to configure) PIM Hello interval or IGMP Query Interval (Which ever 189 is higher) it SHOULD start propagating its original configured DR 190 priority. 192 Even though a new PIM router propagating its priority as 0, it MUST 193 start building a multicast tree towards source / RP, This is So that 194 traffic loss could be minimized once it starts sending Hello with 195 configured DR priority. 197 For a brief amount of time, there would be multiple copies of flows 198 present in the multicast core, but a user SHOULD be able to configure 199 whether to send hello with 0 priority or a configured priority. 200 Depending on the application tolerance (Traffic loss Vs Extra traffic 201 in core) the operator can choose option whichever is suitable for 202 network. 204 After a PIM Hello or IGMP Query interval, the network would get 205 stable with only one DR and one BDR. 207 4.4.2. New PIM router eligible to be PIM BDR on shared LAN 209 It SHOULD follow the exact same procedure defined in the previous 210 section. 212 4.4.3. New PIM router is not eligible to be PIM DR or BDR on shared LAN 214 First a PIM Hello MUST be sent with priority 0. Once it has gotten 215 Hello from other PIM neighbors, it knows that it is not eligible to 216 be PIM DR or BDR. It MUST send configured PIM DR priority 217 immediately. It MUST not wait for next hello interval. 219 4.5. Initial case, All new PIM router coming up in shared LAN 221 In this case, initially each of the PIM routers would send Hellos 222 with priorities of 0. If a PIM router receives all Hellos with 223 priorities 0, it MUST send out a Hello with a configured PIM DR 224 priority. Since it is initial startup case, it would take up to one 225 Hello interval to converge. 227 4.6. Benefit 229 1. Easy to implement as it uses an existing PIM procedure to elect 230 DR. 232 2. Does not introduce any new Hello option 234 5. Compatibility 236 6. Manageability Considerations 238 7. IANA Considerations 240 8. Security Considerations 242 9. Acknowledgement 244 The author would like to thank Stig Venaas, Tharak Abraham, Anish 245 Kachinthaya, Anvitha Kachinthaya for helping with original idea. 247 10. Normative References 249 [I-D.ietf-pim-dr-improvement] 250 Zhang, Z., hu, f., Xu, B., and m. mishra, "PIM DR 251 Improvement", draft-ietf-pim-dr-improvement-04 (work in 252 progress), December 2017. 254 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 255 Requirement Levels", BCP 14, RFC 2119, 256 DOI 10.17487/RFC2119, March 1997, 257 . 259 [RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas, 260 "Protocol Independent Multicast - Sparse Mode (PIM-SM): 261 Protocol Specification (Revised)", RFC 4601, 262 DOI 10.17487/RFC4601, August 2006, 263 . 265 [RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., 266 Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent 267 Multicast - Sparse Mode (PIM-SM): Protocol Specification 268 (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March 269 2016, . 271 Author's Address 273 Mankamana Mishra 274 Cisco Systems 275 821 Alder Drive, 276 MILPITAS, CALIFORNIA 95035 277 UNITED STATES 279 Email: mankamis@cisco.com