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Kumar 3 Internet-Draft Ericsson 4 Intended status: Standards Track May 23, 2017 5 Expires: November 24, 2017 7 Procedures to handle duplicate Route Targets (RT) received by a BGP 8 Speaker 9 draft-anup-idr-bgp-duplicate-rt-00 11 Abstract 13 This document describes why duplicate suppression should not be 14 applied to BGP Route Target (RT) Address Family. It also explains 15 the problems incurred if duplicate suppression is applied to BGP 16 route constraints AF 18 Requirements Language 20 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 21 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 22 document are to be interpreted as described in RFC 2119 [RFC2119] . 24 Status of This Memo 26 This Internet-Draft is submitted in full conformance with the 27 provisions of BCP 78 and BCP 79. 29 Internet-Drafts are working documents of the Internet Engineering 30 Task Force (IETF). Note that other groups may also distribute 31 working documents as Internet-Drafts. The list of current Internet- 32 Drafts is at http://datatracker.ietf.org/drafts/current/. 34 Internet-Drafts are draft documents valid for a maximum of six months 35 and may be updated, replaced, or obsoleted by other documents at any 36 time. It is inappropriate to use Internet-Drafts as reference 37 material or to cite them other than as "work in progress." 39 This Internet-Draft will expire on November 24, 2017. 41 Copyright Notice 43 Copyright (c) 2017 IETF Trust and the persons identified as the 44 document authors. All rights reserved. 46 This document is subject to BCP 78 and the IETF Trust's Legal 47 Provisions Relating to IETF Documents 48 (http://trustee.ietf.org/license-info) in effect on the date of 49 publication of this document. Please review these documents 50 carefully, as they describe your rights and restrictions with respect 51 to this document. Code Components extracted from this document must 52 include Simplified BSD License text as described in Section 4.e of 53 the Trust Legal Provisions and are provided without warranty as 54 described in the Simplified BSD License. 56 Table of Contents 58 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 59 2. Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 60 2.1. Summary of the Problem . . . . . . . . . . . . . . . . . 3 61 3. Problem scenario - An Example . . . . . . . . . . . . . . . . 3 62 4. Existing workaround for the above problem . . . . . . . . . . 4 63 5. Solution to the Problem . . . . . . . . . . . . . . . . . . . 4 64 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 4 65 7. Security Considerations . . . . . . . . . . . . . . . . . . . 4 66 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 67 9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 5 68 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 5 69 10.1. Normative References . . . . . . . . . . . . . . . . . . 5 70 10.2. Informative References . . . . . . . . . . . . . . . . . 5 71 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5 73 1. Introduction 75 Address families like ipv4 unicast are used for exchange of routing 76 or reachability information. Receipt of an ipv4 unicast update by 77 router R means that the peer has the ipv4 route and hence, has sent 78 it to R, while the receiving router R computes bestpath and uses the 79 route for forwarding. 81 With respect to receiving ipv4 unicast update, we have two 82 possibilities: 84 1) The receiving router does not have the original route in its 85 database. It treats the update as fresh update. So, the received 86 ipv4 unicast update is processed and downloaded for forwarding. 88 2) The receiving router already has the route in its database. It 89 treats the update as duplicate and drops it. It is guaranteed by 90 BGP base protocol that the receiver had processed and 91 installed the route when the earlier update was seen, and hence it 92 can drop the duplicate ipv4 unicast update. Even if the duplicate 93 is processed again and installed again, there is no problem with 94 duplicate processing and installation. 96 2. Problem 98 This section explains the problem when duplicate suppression is 99 applied to BGP updates carrying Route Targets (RT) Address Family 100 information. 102 RT address family is used to exchange VPN subscription information. 103 Receipt of an RT update means that the sender is interested in 104 getting vpn routes from this router. This router is expected to send 105 matching vpn routes in response. Which means, receipt of an RT 106 update, unlike ipv4 unicast update, does not end with local 107 installation of route, but also necessarily entails sending vpn 108 routes in response. 110 Like before, we have two cases to analyze with respect to receiving 111 duplicate RT updates: 113 1) The receiving router does not have earlier RT in its database. 114 It treats the RT as fresh update, and it sends vpn routes in 115 response. 117 2) The receiving router already has the RT in its database. It 118 treats the incoming RT as duplicate and drops it. But, when the 119 receiver gets the duplicate RT, whether the sender has vpn routes 120 or not, is not known at the receiver side. So, dropping the 121 duplicate RT without sending vpn routes in response, is a problem. 123 2.1. Summary of the Problem 125 When a duplicate RT is received, it is not guaranteed that the sender 126 of the RT has the required vpn routes. So the receiver cannot choose 127 to ignore an RT as duplicate, because unlike Ipv4 unicast route, an 128 RT indicates a subscription or a want of vpn routes and the receiver 129 does not know whether the sender has the vpn routes or not. 131 3. Problem scenario - An Example 133 First time when the import RT is configured the sender will not 134 have vpn routes, and it sends the RT to its peers, thereby 135 conveying its want of vpn routes. 137 The receiver also sees this RT coming from the sender for the 138 first time, and It sends vpn routes in response to the sender of 139 the RT. 141 Now, certain Destructive operations can lead to cleanup of vpn 142 routes. Example: Remove and add of vpn configurations, 'without' 143 affecting bgp peer session state. 145 Here, due to removal of vpn config, the sender will cleanup the 146 vpn routes. 148 Then, due to quick addition of vpn config, the sender will request 149 for vpn routes by sending all the configured RTs. 151 But, the receiver still has the earlier RTs that was sent by the 152 peer. So, the receiver treats the RTs as duplicate and drops 153 them. 155 Thus no vpn routes are sent to the sender 157 4. Existing workaround for the above problem 159 Implementations solve this problem at the sender side by sending a 160 request for Route refresh (known as a bgp soft in request), after any 161 modification to vpn configuration. But, this is only a workaround. 162 The real problem is in the way bgp treats received RT. The 163 corrective measure should be at the receiver's side, by sending out 164 vpn routes in response, though the RT might be a duplicate. Further, 165 when the receiver has the ability to use RTs to walk only the 166 required VPN tables with an objective to avoid full walk, sending a 167 request for full route refresh will prevent the receiver from 168 utilizing its ability to walk required VPN tables for the RT. So, 169 sending a request for route refresh not only masks the problem in 170 2.1, but also leads to inefficient vpn walks at the sender capable of 171 selective vpn update generation per received RT. 173 5. Solution to the Problem 175 When the received RT is a duplicate, the receiver should respond with 176 vpn routes, rather than simply dropping the duplicate RT. 178 6. Acknowledgments 180 The author would like to thank P. Muthu and team for their 181 comments and review. 183 7. Security Considerations 185 There are no additional security considerations than the base BGP 186 RFC. 188 8. IANA Considerations 190 This document has no actions for IANA. 192 9. Contributors 194 10. References 196 10.1. Normative References 198 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 199 Requirement Levels", BCP 14, RFC 2119, 200 DOI 10.17487/RFC2119, March 1997, 201 . 203 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 204 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 205 DOI 10.17487/RFC4271, January 2006, 206 . 208 10.2. Informative References 210 [RFC4684] Marques, P., Bonica, R., Fang, L., Martini, L., Raszuk, 211 R., Patel, K., and J. Guichard, "Constrained Route 212 Distribution for Border Gateway Protocol/MultiProtocol 213 Label Switching (BGP/MPLS) Internet Protocol (IP) Virtual 214 Private Networks (VPNs)", RFC 4684, DOI 10.17487/RFC4684, 215 November 2006, . 217 Author's Address 219 Anup Kumar T 220 Ericsson India Pvt Ltd 221 Ferns Icon, Doddanakkundi, Mahadevapura 222 Bengaluru 560037 223 India 225 Email: anupkumar.t@ericsson.com