Inter-Domain Routing T. Kumar Internet-Draft Ericsson Intended status: Standards Track May 23, 2017 Expires: November 24, 2017 Procedures to handle duplicate Route Targets (RT) received by a BGP Speaker draft-anup-idr-bgp-duplicate-rt-00 Abstract This document describes why duplicate suppression should not be applied to BGP Route Target (RT) Address Family. It also explains the problems incurred if duplicate suppression is applied to BGP route constraints AF Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119] . Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on November 24, 2017. Copyright Notice Copyright (c) 2017 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of Kumar Expires November 24, 2017 [Page 1] Internet-Draft BGP Duplicate Route Targets May 2017 publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1. Summary of the Problem . . . . . . . . . . . . . . . . . 3 3. Problem scenario - An Example . . . . . . . . . . . . . . . . 3 4. Existing workaround for the above problem . . . . . . . . . . 4 5. Solution to the Problem . . . . . . . . . . . . . . . . . . . 4 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 4 7. Security Considerations . . . . . . . . . . . . . . . . . . . 4 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 5 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 5 10.1. Normative References . . . . . . . . . . . . . . . . . . 5 10.2. Informative References . . . . . . . . . . . . . . . . . 5 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5 1. Introduction Address families like ipv4 unicast are used for exchange of routing or reachability information. Receipt of an ipv4 unicast update by router R means that the peer has the ipv4 route and hence, has sent it to R, while the receiving router R computes bestpath and uses the route for forwarding. With respect to receiving ipv4 unicast update, we have two possibilities: 1) The receiving router does not have the original route in its database. It treats the update as fresh update. So, the received ipv4 unicast update is processed and downloaded for forwarding. 2) The receiving router already has the route in its database. It treats the update as duplicate and drops it. It is guaranteed by BGP base protocol that the receiver had processed and installed the route when the earlier update was seen, and hence it can drop the duplicate ipv4 unicast update. Even if the duplicate is processed again and installed again, there is no problem with duplicate processing and installation. Kumar Expires November 24, 2017 [Page 2] Internet-Draft BGP Duplicate Route Targets May 2017 2. Problem This section explains the problem when duplicate suppression is applied to BGP updates carrying Route Targets (RT) Address Family information. RT address family is used to exchange VPN subscription information. Receipt of an RT update means that the sender is interested in getting vpn routes from this router. This router is expected to send matching vpn routes in response. Which means, receipt of an RT update, unlike ipv4 unicast update, does not end with local installation of route, but also necessarily entails sending vpn routes in response. Like before, we have two cases to analyze with respect to receiving duplicate RT updates: 1) The receiving router does not have earlier RT in its database. It treats the RT as fresh update, and it sends vpn routes in response. 2) The receiving router already has the RT in its database. It treats the incoming RT as duplicate and drops it. But, when the receiver gets the duplicate RT, whether the sender has vpn routes or not, is not known at the receiver side. So, dropping the duplicate RT without sending vpn routes in response, is a problem. 2.1. Summary of the Problem When a duplicate RT is received, it is not guaranteed that the sender of the RT has the required vpn routes. So the receiver cannot choose to ignore an RT as duplicate, because unlike Ipv4 unicast route, an RT indicates a subscription or a want of vpn routes and the receiver does not know whether the sender has the vpn routes or not. 3. Problem scenario - An Example First time when the import RT is configured the sender will not have vpn routes, and it sends the RT to its peers, thereby conveying its want of vpn routes. The receiver also sees this RT coming from the sender for the first time, and It sends vpn routes in response to the sender of the RT. Now, certain Destructive operations can lead to cleanup of vpn routes. Example: Remove and add of vpn configurations, 'without' affecting bgp peer session state. Kumar Expires November 24, 2017 [Page 3] Internet-Draft BGP Duplicate Route Targets May 2017 Here, due to removal of vpn config, the sender will cleanup the vpn routes. Then, due to quick addition of vpn config, the sender will request for vpn routes by sending all the configured RTs. But, the receiver still has the earlier RTs that was sent by the peer. So, the receiver treats the RTs as duplicate and drops them. Thus no vpn routes are sent to the sender 4. Existing workaround for the above problem Implementations solve this problem at the sender side by sending a request for Route refresh (known as a bgp soft in request), after any modification to vpn configuration. But, this is only a workaround. The real problem is in the way bgp treats received RT. The corrective measure should be at the receiver's side, by sending out vpn routes in response, though the RT might be a duplicate. Further, when the receiver has the ability to use RTs to walk only the required VPN tables with an objective to avoid full walk, sending a request for full route refresh will prevent the receiver from utilizing its ability to walk required VPN tables for the RT. So, sending a request for route refresh not only masks the problem in 2.1, but also leads to inefficient vpn walks at the sender capable of selective vpn update generation per received RT. 5. Solution to the Problem When the received RT is a duplicate, the receiver should respond with vpn routes, rather than simply dropping the duplicate RT. 6. Acknowledgments The author would like to thank P. Muthu and team for their comments and review. 7. Security Considerations There are no additional security considerations than the base BGP RFC. 8. IANA Considerations This document has no actions for IANA. Kumar Expires November 24, 2017 [Page 4] Internet-Draft BGP Duplicate Route Targets May 2017 9. Contributors 10. References 10.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A Border Gateway Protocol 4 (BGP-4)", RFC 4271, DOI 10.17487/RFC4271, January 2006, . 10.2. Informative References [RFC4684] Marques, P., Bonica, R., Fang, L., Martini, L., Raszuk, R., Patel, K., and J. Guichard, "Constrained Route Distribution for Border Gateway Protocol/MultiProtocol Label Switching (BGP/MPLS) Internet Protocol (IP) Virtual Private Networks (VPNs)", RFC 4684, DOI 10.17487/RFC4684, November 2006, . Author's Address Anup Kumar T Ericsson India Pvt Ltd Ferns Icon, Doddanakkundi, Mahadevapura Bengaluru 560037 India Email: anupkumar.t@ericsson.com Kumar Expires November 24, 2017 [Page 5]