IDR Working Group R.
RaszukRaszuk, Ed. Internet-Draft Mirantis Inc.Bloomberg LP Intended status: Standards Track C. Cassar Expires: January 3,July 11, 2016 Cisco Systems E. Aman TeliaSonera B. Decraene S. Litkowski Orange July 2, 2015K. Wang Juniper Networks January 8, 2016 BGP Optimal Route Reflection (BGP-ORR) draft-ietf-idr-bgp-optimal-route-reflection-10draft-ietf-idr-bgp-optimal-route-reflection-11 Abstract This document proposes a solution for BGP route reflectors to facilitateallow them to choose the application of closest exit point policy (hot potato routing)best path their clients would have chosen under the same conditions, without requiring further state or any new features to be placed on the RRclients. This facilitates, for example, best exit point policy (hot potato routing). This solution is primarily applicable in deployments using centralized route reflectors. The solution relies upon all route reflectors learning all paths which are eligible for consideration for hot potato routing.consideration. Best path selection is performed in each route reflector based on a configured virtual location in the IGP. The location can be the same for all clients or different per peer/update group or per neighbour.peer. Best path selection can also be performed based on user configured policies in each route reflector. 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 January 3,July 11, 2016. Copyright Notice Copyright (c) 20152016 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 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 1.1. Problem Statement . . . . . . . . . . . . . . . . . . . . 23 1.2. Existing/Alternative Solutions . . . . . . . . . . . . . 34 2. Proposed Solution .Solutions . . . . . . . . . . . . . . . . . . . . . 4 2.1. Client's Perspective IGP Based Best Path Selection . . . 5 2.2. Client's Perspective Policy Based Best Path Selection . . 6 2.3. Solution Interactions . . . . . . . . . . . . . . . . . . 6 3. CPU and Memory Scalability . . . . . . . . . . . . . . . . . 57 4. Advantages and Deployment Considerations . . . . . . . . . . 68 5. Security Considerations . . . . . . . . . . . . . . . . . . . 69 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 79 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 79 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 79 8.1. Normative References . . . . . . . . . . . . . . . . . . 79 8.2. Informative References . . . . . . . . . . . . . . . . . 79 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 810 1. Introduction There are three types of BGP deployments within Autonomous Systems today: full mesh, confederations and route reflection. BGP route reflection [RFC4456] is the most popular way to distribute BGP routes between BGP speakers belonging to the same Autonomous System. In some situations, this method suffers from non-optimal path selection. 1.1. Problem Statement [RFC4456] asserts that, because the Interior Gateway Protocol (IGP) cost to a given point in the network will vary across routers, "the route reflection approach may not yield the same route selection result as that of the full IBGP mesh approach." One practical implication of this assertion is that the deployment of route reflection may thwart the ability to achieve hot potato routing. Hot potato routing attempts to direct traffic to the closestbest AS egressexit point in cases where no higher priority policy dictates otherwise. As a consequence of the route reflection method, the choice of exit point for a route reflector and its clients will be the egressexit point closest tobest for the route reflector - not necessarily the one closest tobest for the RR clients. Section 11 of [RFC4456] describes a deployment approach and a set of constraints which, if satisfied, would result in the deployment of route reflection yielding the same results as the iBGP full mesh approach. This deployment approach makes route reflection compatible with the application of hot potato routing policy. In accordance with these design rules, route reflectors have traditionally often been deployed in the forwarding path and carefully placed on the POP to core boundaries. The evolving model of intra-domain network design has enabled deployments of route reflectors outside of the forwarding path. Initially this model was only employed for new address families, e.g. L3VPNs and L2VPNs. This model has been gradually extended to other BGP address families including IPv4 and IPv6 Internet using either native routing or 6PE. In such environments, hot potato routing policy remains desirable. Route reflectors outside of the forwarding path can be placed on the POP to core boundaries, but they are often placed in arbitrary locations in the core of large networks. Such deployments suffer from a critical drawback in the context of best path selection: A route reflector with knowledge of multiple paths for a given prefix will typically pick its best path and only advertise that best path to its clients. If the best path for a prefix is selected on the basis of an IGP tie break, the path advertised will be the exit point closest to the route reflector. But the clients will be in a different place in the network topology than the route reflector. In networks where the route reflectors are not in the forwarding path, this difference will be even more acute. Beside this, there are also deployment scenarios where service providers want to have more control of choosing the exit points for clients based on other factors like traffic type, traffic load, etc. This further complicated the issue and makes it less likely for the route reflector to select the best path from the client's perspective. It follows that the best path chosen by the route reflector is not necessarily the same as the path which would have been chosen by the client if the client had considered the same set of candidate paths as the route reflector. The path chosen by the client would have guaranteed the lowest cost and delay trajectory through the network.1.2. Existing/Alternative Solutions Eliminating the IGP distance to the BGP nexthop as a tie breaker on centralized route reflectors does not address the issue. Ignoring IGP distance to the BGP next hop results in the tie breaking procedure contributing the best path by differentiating between paths using attributes otherwise considered less important than IGP cost to the BGP nexthop.One possible valid solution or workaround to the best path selection problem requires sending all domain external paths from the RR to all its clients. This approach suffers the significant drawback of pushing a large amount of BGP state to all edge routers. Many networks receive full Internet routing information in a large number of locations. This could easily result in tens of paths for each prefix that would need to be distributed to clients. Notwithstanding this drawback, there are a number of reasons for sending more than just the single best path to the clients. Improved path diversity at the edge is a requirement for fast connectivity restoration, and a requirement for effective BGP level load balancing. In practical terms, add/diverse path deployments are expected to result in the distribution of 2, 3 or n (where n is a small number) 'good' paths rather than all domain external paths. While the route reflector chooses one set of n paths and distributes those same n paths to all its route reflector clients, those n paths may not be the right n paths for all clients. In the context of the problem described above, those n paths will not necessarily include the closest egressbest exit point out of the network for each route reflector client. The mechanisms proposed in this document are likely to be complementary to mechanisms aimed at improving path diversity. 2. Proposed SolutionSolutions The coregoal of the proposed solutionthis document is the ability for an operatorto specify onallow a perroute reflector basis or per peer/update group basis or per neighbour basisto choose the virtual IGPbest path the client would have chosen had the client considered the same set of candidate paths the reflector has available. For purposes of route selection, the perspective of a client can differ from that of a route reflector or another client in two distinct ways: it can, and usually will, have a different position in the IGP topology, and it can have a different routing policy. These correspond to the issues described earlier. Accordingly, we propose two distinct modifications to the best path algorithm, to address these two distinct factors. A route reflector can implement either or both of the modifications, as needed in order to allow it to choose the best path the client would have chosen had the client considered the same set of candidate paths. Both modifications rely upon all route reflectors learning all paths which are eligible for consideration. In order to satisfy this requirement, path diversity enhancing mechanisms such as ADD-PATH/ diverse paths may need to be deployed between route reflectors. A significant advantage of these approaches is that the RR clients do not need to run new software or hardware. 2.1. Client's Perspective IGP Based Best Path Selection The core of this solution is the ability for an operator to specify on a per route reflector basis or per peer/update group basis or per peer basis the virtual IGP location placement of the route reflector. This enables having a given group of clients toreceive routes with optimal distance to the next hops from the position of the configured virtual IGP location. This also provides for freedom onof route reflector location and allows transient or permanent migration of such network control plane function to optimal location. The choice of specific granularity is left to the implementation decision. An implementation is considered compliant with the document if it supports at least one listed grouping of virtual IGP placement. By optimal we refer inIn this document we refer to optimal as the decision made during best path selection at the IGP metric to BGP next hop comparison step. This documentapproach does not apply to path selection preference based other policy steps and provisions. The solution relies upon all route reflectors learning all paths which are eligible for consideration for hot potato routing. In order to satisfycomputation of the virtual IGP location with any of the above described granularity is outside of the scope of this requirement, path diversity enhancing mechanisms such as ADD-PATH/diversedocument. The operator may configure it manually, implementation may automate it based on specified heuristic or it can be computed centrally and configured by an external system. The solution does not require any BGP or IGP protocol changes as required changes are contained within the RR implementation. The solution applies to NLRIs of all address families which can be route reflected. 2.2. Client's Perspective Policy Based Best Path Selection Optimal route reflection based on virtual IGP location could reflect the best path to the client from IGP cost perspective. However, there are also cases where the client might want best path from perspectives beyond IGP cost. Examples include, but not limited to: o Select the best path for the clients from a traffic engineering perspective. o Dedicate certain exit points for certain ingress points. The solution proposed here is to allow the user to apply a general policy to select a subset of exit points as the candidate exit points for its clients. For a given client, the policy should also allow service providers to select different candidate exit points for different address families. Regular path selection, including client's perspective IGP based best path selection stated above, will be applied to the candidate paths to select the final paths to advertise to the clients. The policy is applied on the route reflector on behalf of its clients. This way, the route reflector will be able to reflect only the optimal paths to the clients. An additional advantage of this approach is that configuration need only be done on a small number of route reflectors rather than a significantly larger number of clients. 2.3. Solution Interactions Depending on the actual deployment scenarios, service providers may configure IGP based optimal route reflection or policy based optimal route reflection. It's also possible to configure both approaches together. In that case, policy based optimal route reflection will be applied first to select the candidate paths. Subsequently, IGP based optimal route reflection will be applied on top of the candidate paths to select the final path to advertise to the client. The expected use case for optimal route reflection is to avoid reflecting all paths to the client because the client either does not support add-paths or does not have the capacity to process all of the paths. Typically the route reflector would just reflect a single optimal route to the client. However, the solutions MUST NOT prevent reflecting more than one optimal path to the client; the client may want path diversity for load balancing or fast restoration. In case add-path and optimal route reflection are configured together, the route reflector MUST reflect n optimal paths to a client, where n is the add-path count. The most complicated scenario is where add-path is configured together with both IGP based and policy based optimal route reflection. In this scenario, the policy based optimal route reflection will be applied first to select the candidate paths. Subsequently, IGP based optimal route reflection will be applied on top of the candidate paths to select the best n paths may needto be deployed betweenadvertise to the client. In IGP based optimal route reflectors. A significant advantage of this approach is thatreflection, even though the RR clients do not needvirtual IGP location could be specified on a per route reflector basis or per peer group basis or per peer basis, in reality, it's most likely to run new softwarebe specified per peer group basis. All clients with the same or hardware. The computation ofsimilar IGP location can be grouped into the same peer group. A virtual IGP location with any of the above described granularityis outside ofthen specified for the scope of this document.peer group. The operator may configure it manually, implementation may automate it based onvirtual location is usually specified heuristicas the location of one of the clients from the peer group or it can be computed centrally and configured byan external system. The solution does not require any BGP or IGP protocol changes as required changes are contained withinABR to the RR implementation. The solution appliesarea where clients are located. Also, one or more backup virtual location SHOULD be allowed to NLRIs of all address families which canbe specified for redundancy. Implementations may wish to take advantage of peer group mechanisms in order to provide for better scalability of optimal route reflected.reflector client groups with similar properties. 3. CPU and Memory Scalability DeterminingFor IGP based optimal route reflection, determining the shortest path and associated cost between any two arbitrary points in a network based on the IGP topology learned by a router is expected to add some extra cost in terms of CPU resources. However SPF tree generation code is now implemented efficiently in a number of implementations, and therefore this is not expected to be a major drawback. The number of SPTs computed is expected to be of the order of the number of clients of an RR whenever a topology change is detected. Advanced optimizations like partial and incremental SPF may also be exploited. The number of SPTs computed is expected to be higher but comparable to some existing deployed features such as (Remote) Loop Free Alternate which computes a (r)SPT per IGP neighbor. For policy based optimal route reflection, there will be some overhead to apply the policy to select the candidate paths. This overhead is comparable to existing BGP export policies therefore should be manageable. By the nature of route reflection, the number of clients can be split arbitrarily by the deployment of more route reflectors for a given number of clients. While this is not expected to be necessary in existing networks with best in class route reflectors available today, this avenue to scaling up the route reflection infrastructure would be available. If we consider the overall network wide cost/benefit factor, the only alternative to achieve the same level of optimality would require significantly increasing state on the edges of the network, which, in turn,network. This will consume CPU and memory resources on all BGP speakers in the network. Building this client perspective into the route reflectors seems appropriate. 4. Advantages and Deployment Considerations The solutionsolutions described providesprovide a model for integrating the client perspective into the best path computation for RRs. More specifically, the choice of BGP path factors in either the IGP metriccost between the client and the nexthop, rathernexthop (rather than the distance from the RR to the nexthop. This solutionnexthop) or user configured policies. These solutions can be deployed in traditional hop-by-hop forwarding networks as well as in end-to-end tunneled environments. In the networks where there are multiple route reflectors and hop-by-hop forwarding without encapsulation, such optimizations should be enabled in a consistent way on all route reflectors. Otherwise clients may receive an inconsistent view of the network and in turn lead to intra-domain forwarding loops. With this approach, an ISP can effect a hot potato routing policy even if route reflection has been moved from the forwarding plane and hop-by-hop switching has been replaced by end-to-end MPLS or IP encapsulation. As per above, the approach reducesthese approaches reduce the amount of state which needs to be pushed to the edge of the network in order to perform hot potato routing. The memory and CPU resource required at the edge of the network to provide hot potato routing using this approachthese approaches is lower than what would be required in order to achieve the same level of optimality by pushing and retaining all available paths (potentially 10s) per each prefix at the edge. The proposal allowsproposals allow for a fast and safe transition to a BGP control plane with centralized route reflection without compromising an operator's closest exit operational principle. This enables edge-to- edge LSP/IP encapsulation for traffic to IPv4 and IPv6 prefixes. Regarding the client's IGP best-path selection, it should be self evident that this solution does not interfere with policies enforced above IGP tie breaking in the BGP best path algorithm. 5. Security Considerations No new security issues are introduced to the BGP protocol by this specification. 6. IANA Considerations This document does not request any IANA allocations. 7. Acknowledgments Authors would like to thank Keyur Patel, Eric Rosen, Clarence Filsfils, Uli Bornhauser, Russ White, Jakob Heitz, Mike Shand andShand, Jon MitchellMitchell, John Scudder, Jeff Haas, and Martin Djernaes for their valuable input. 8. References 8.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.1997, <http://www.rfc-editor.org/info/rfc2119>. [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 2006.2006, <http://www.rfc-editor.org/info/rfc4271>. [RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended Communities Attribute", RFC 4360, DOI 10.17487/RFC4360, February 2006.2006, <http://www.rfc-editor.org/info/rfc4360>. [RFC5492] Scudder, J. and R. Chandra, "Capabilities Advertisement with BGP-4", RFC 5492, DOI 10.17487/RFC5492, February 2009.2009, <http://www.rfc-editor.org/info/rfc5492>. 8.2. Informative References [I-D.ietf-idr-add-paths] Walton, D., Retana, A., Chen, E., and J. Scudder, "Advertisement of Multiple Paths in BGP", draft-ietf-idr- add-paths-10add-paths-13 (work in progress), October 2014.December 2015. [RFC1997] Chandrasekeran,Chandra, R., Traina, P., and T. Li, "BGP Communities Attribute", RFC 1997, DOI 10.17487/RFC1997, August 1996.1996, <http://www.rfc-editor.org/info/rfc1997>. [RFC1998] Chen, E. and T. Bates, "An Application of the BGP Community Attribute in Multi-home Routing", RFC 1998, DOI 10.17487/RFC1998, August 1996.1996, <http://www.rfc-editor.org/info/rfc1998>. [RFC4384] Meyer, D., "BGP Communities for Data Collection", BCP 114, RFC 4384, DOI 10.17487/RFC4384, February 2006.2006, <http://www.rfc-editor.org/info/rfc4384>. [RFC4456] Bates, T., Chen, E., and R. Chandra, "BGP Route Reflection: An Alternative to Full Mesh Internal BGP (IBGP)", RFC 4456, DOI 10.17487/RFC4456, April 2006.2006, <http://www.rfc-editor.org/info/rfc4456>. [RFC4893] Vohra, Q. and E. Chen, "BGP Support for Four-octet AS Number Space", RFC 4893, DOI 10.17487/RFC4893, May 2007.2007, <http://www.rfc-editor.org/info/rfc4893>. [RFC5283] Decraene, B., Le Roux, JL., and I. Minei, "LDP Extension for Inter-Area Label Switched Paths (LSPs)", RFC 5283, DOI 10.17487/RFC5283, July 2008.2008, <http://www.rfc-editor.org/info/rfc5283>. [RFC5668] Rekhter, Y., Sangli, S., and D. Tappan, "4-Octet AS Specific BGP Extended Community", RFC 5668, DOI 10.17487/RFC5668, October 2009.2009, <http://www.rfc-editor.org/info/rfc5668>. [RFC5714] Shand, M. and S. Bryant, "IP Fast Reroute Framework", RFC 5714, DOI 10.17487/RFC5714, January 2010.2010, <http://www.rfc-editor.org/info/rfc5714>. [RFC6774] Raszuk, R., Ed., Fernando, R., Patel, K., McPherson, D., and K. Kumaki, "Distribution of Diverse BGP Paths", RFC 6774, DOI 10.17487/RFC6774, November 2012.2012, <http://www.rfc-editor.org/info/rfc6774>. Authors' Addresses Robert Raszuk Mirantis Inc. 615 National Ave. #100 Mt View, CA 94043(editor) Bloomberg LP 731 Lexington Ave New York City, NY 10022 USA Email: firstname.lastname@example.org Christian Cassar Cisco Systems 10 New Square Park Bedfont Lakes, FELTHAM TW14 8HA UK Email: email@example.com Erik Aman TeliaSonera Marbackagatan 11 Farsta SE-123 86 Sweden Email: firstname.lastname@example.org Bruno Decraene Orange 38-40 rue du General Leclerc Issy les Moulineaux cedex 9 92794 France Email: email@example.com Stephane Litkowski Orange 9 rue du chene germain Cesson Sevigne 35512 France Email: firstname.lastname@example.org Kevin Wang Juniper Networks 10 Technology Park Drive Westford, MA 01886 USA Email: email@example.com