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BGP Diverse Paths

BGP Diverse Paths. draft -ietf-grow-diverse-bgp-paths-dist-02. Keyur Patel. RIPE 61 , November 2010, Rome, Italy. Motivation. BGP protocol defined in RFC4271 provides a mechanism to announce only a single path aka a BGP bestpath

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BGP Diverse Paths

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  1. BGP Diverse Paths draft-ietf-grow-diverse-bgp-paths-dist-02 • KeyurPatel • RIPE 61, November 2010, Rome, Italy

  2. Motivation • BGP protocol defined in RFC4271 provides a mechanism to announce only a single path aka a BGP bestpath • Announcement of multiple paths within BGP is gradually becoming a requirement • Used for BGP Fast Convergence • Different solutions available to announce multiple paths with BGP • BGP Full mesh + BGP Best External • BGP Additional Paths • Different RD approach in BGP VPNs • BGP Diverse paths

  3. BGP Full Mesh + BGP Best External • BGP full mesh explained at length in BGP RFC 4271 • Assures path diversity in hot potato routing • Needs BGP Best External support for cold potato routing • BGP Best External explained at length in draft-ietf-idr-best-external-02.txt • All BGP speaking routers establish peering with each other • Results in TCP state explosion • BGP can store as many paths as sessions

  4. BGP Add Paths • BGP Add paths explained at length in draft-walton-bgp-addpaths-06.txt • Mechanism to announce multiple paths over a single neighbor session • New BGP protocol encoding and a capability • Requires a network-wide upgrade • Operators need to figure out how many paths and what paths to announce • Can the edge router handle a load of more than 2 paths?

  5. VPNs & Different RD Approach • L3VPNs can announce multiple paths using different RD approach • Implementation tweak: - SPs can configure multiple RDs for their multi-homed customers • Each unique RD creates separate set of customer prefixes and thereby ensures multiple paths • Works well and deployed in most of the L3VPN environment • No reason to look into BGP Add Paths or BGP Diverse paths

  6. BGP Diverse Paths • RR based solution • Does NOT require an upgrade of an entire network • Does not require any protocol changes • Applicable to all BGP AFI/SAFIs • Targeted mostly for IP hop-by-hop as well as tunneled networks • Diverse paths are announced either using • Shadow RRs that calculate only diverse paths • Shadow sessions that announce only diverse paths

  7. BGP Diverse Paths (RR Functionality) • RRs need to pre-compute diverse paths as part of its bestpath processing • RR can operate as if it was a diverse/backup RR and only announce diverse paths to its configured neighbors • IGP metric check needs to be disabled in order to deterministically compute diverse paths • Alternatively RRs can track session types and announce appropriate diverse path accordingly • Requires configuration of new addresses for diverse path sessions (one address per nth diverse path announced to all BGP neighbors) • RRs in forwarding plane needs to pre-compute and install diverse paths in its RIB and FIB • Covers hot potato routing as well as cold potato routing • RR needs to account for additional diverse path computation

  8. Diverse Paths PE/ASBR Functionality • PE/ASBR may need configure additional sessions with RRs • Does NOT require any software upgrade • Can reuse its existing peering address for diverse path sessions • PE/ASBR treats diverse paths as just another BGP path received • PE/ASBR can use diverse paths to pre-compute and install backup paths in RIB and FIB • PE/ASBR needs to account for • Additional sessions to enable diverse paths • Additional memory to store diverse paths

  9. RR Deployment Models Today’s case: Diverse sessions: Diverse RR: 10/8 - P1*, P2 .... 10/8 - P1*, P2 .... 10/8 - P1*, P2 .... RR1 RR2 RR1 RR2 RR1 RR2 s1 s2 PE/ASBR PE/ASBR PE/ASBR 10/8 - P1 via RR1 - P1 via RR2 10/8 - P1 via RR1 - P2 via RR2 10/8 - P1 via RR1 - P1 via RR2 s1 - P2 via RR2 s2 RR1 & RR2 same IGP location or IGP metric ignore in best path Possible to peer both sessions s1 and s2 to the same loopback on PE/ASBR.

  10. IBGP Network With Flat Igp & Multiple RR Clusters P1/nh ASBR1 PE4 P1 RR1 P1/nh ASBR1 P2 ASBR2 P1 P1, P2, P3a, P3b ASBR1 RR2 PE2 P1/nh ASBR1 PE1 P1/nh ASBR1 P1/nh ASBR1 P1/nh ASBR1 ASBR3a ASBR3b P3a P3b

  11. IBGP Network With Flat Igp, Multiple RR & Shadow RR Clusters P2/nh ASBR2 P1/nh ASBR1 PE4 • RR1’ and RR2’ are shadow RRs • RR1, RR1’ & RR2, RR2’ are in different • clusters • They are configured to calculate and • advertisediverse path to it’s clients • They can do it on a per AFI/SAFI basis • Same IGP metric as best RRs or IGP metric • disabled on both • P1 overall best and P2 second best/diverse P1 RR1 P1/nh ASBR1 P2 P1, P2 ASBR2 RR1’ P2/nh ASBR2 P1 P1, P2, P3a, P3b ASBR1 RR2 PE2 • Deployment Considerations: • No upgrade of any existing PE/ASBR is • required • Additional IBGP session per eachdiverse • path • Additional shadow RR per cluster • Works within flat domain or within each • area of hierarchical network P2, P3a, P3b P1/nh ASBR1 RR2’ P2/nh ASBR2 PE1 P1/nh ASBR1 P2/nh ASBR2 P1/nh ASBR1 P1/nh ASBR1 ASBR3a ASBR3b P2/nh ASBR2 P2/nh ASBR2 P3a P3b

  12. IBGP Network With Flat Igp And Multiple RR Clusters P1/nh ASBR1 P2/nh ASBR2 PE4 • RRs and RRs’ are same RRs • RR1, RR1’ & RR2, RR2’ are in different • clusters • They are configured to calculate and • advertisediversepath to it’s clients on a • per neighbor basis • They can do it on a per AFI/SAFI basis • Same IGP metric as best RRs • P1 overall best, P2 second best/diverse RR1 P1, P2 P1/nh ASBR1 RR1’ P2 ASBR2 P2/nh ASBR2 P1 ASBR1 P1, P2, P3a, P3b RR2 PE2 RR2’ P1/nh ASBR1 P2/nh ASBR2 PE1 P1/nh ASBR1 P2/nh ASBR2 • Deployment Considerations: • No upgrade of any existing PE/ASBR is • required • Additional IBGP sessions per each diverse • path • No additional Shadow RRs required • Works within flat domain or within each • area of hierarchical network P1/nh ASBR1 P1/nh ASBR1 ASBR3a ASBR3b P2/nh ASBR2 P2/nh ASBR2 P3a P3b

  13. Hierarchial RRs PE4 • Each shadow RR is configured to • calculate andadvertise diverse path • to it’s clients (POP RRs) on a • per neighbor basis • They can do it on a per AFI/SAFI basis • Any encapsulation can be used • within each area IP or MPLS (option). • Pop RRs replicate the design in the • same manner RR4a RR4b P1 P2 P3 P1 P2 P3 P2 ASBR2 P1 ASBR1 P1 P2 P3 L2-RR1 RR1a RR2a P1 P2 P3 P1 P2 P3 P1 P2 P3 L2-RR1’ P1 P2 P3 L2-RR1” RR1b RR2b PE1 P1 P2 P3 P1 P2 P3 PE2 P1 P2 P3 P1 P2 P3 RR3a RR3b P3a P3b P3a P3b • Deployment Consideration: • No upgrade of any existing PE/ASBR is • required • Additional IBGP sessions per each • diverse path ASBR3a ASBR3b P3a P3b

  14. Diverse Paths & BGP Best External • Intra-cluster routes may not always get announced with diverse paths • Diverse paths does NOT change any BGP route propagation rules • IBGP network still has multiple diverse paths for a given prefix • Not an issue within a Cluster • Usage of BGP Best External between RRs can assure announcements of intra cluster routes • Reduce number of sessions between full meshed RRs • Achieve higher path diversity within the network

  15. Diverse Paths With Missing Intra-Cluster routes P3a/nh ASBR3a P3b/nh ASBR3b PE4 • RRs and RRs’ are same RRs • RR1, RR1’ & RR2, RR2’ are in different • clusters • They are configured to calculate and • advertisediversepath to it’s clients on a • per neighbor basis • They can do it on a per AFI/SAFI basis • Same IGP metric as best RRs • Cold Potato Routing (Local Prefs win) • P3a overall best, P3b second best/diverse • RR1 and RR1’ got 3 paths • RR2 and RR2’ got 3 paths • Network still has path diversity P3a/nh ASBR3a RR1 P3a, P3b, P1, P3b/nh ASBR3b RR1’ P2 ASBR2 P3a/nh ASBR3a P3b/nh ASBR3b P1 ASBR1 RR2 P3a, P3b, P2 PE2 RR2’ P3a/nh ASBR3a P3b/nh ASBR3b PE1 P3a/nh ASBR3a P3b/nh ASBR3b ASBR3a ASBR3b P3b/nh ASBR3b P3a/nh ASBR3a P3a P3b

  16. BGP Diverse Paths + BGP Best External P3a/nh ASBR3a P3b/nh ASBR3b PE4 • RRs and RRs’ are same RRs • RR1, RR1’ & RR2, RR2’ are in different • clusters • They are configured to calculate and • advertisediversepath to it’s clients on a • per neighbor basis • They can do it on a per AFI/SAFI basis • Same IGP metric as best RRs • Cold Potato Routing (Local Prefs win) • P3a overall best, P3b second best/diverse • RR1 and RR1’ got 3 paths • RR2 and RR2’ got 4 paths • Network still has path diversity P3a/nh ASBR3a RR1 P3a, P3b, P1 P3b/nh ASBR3b RR1’ P2 ASBR2 P3a/nh ASBR3a P3b/nh ASBR3b P1 ASBR1 P3a, P3b, P1, P2 RR2 PE2 RR2’ P3a/nh ASBR3a P3b/nh ASBR3b PE1 P3a/nh ASBR3a P3b/nh ASBR3b ASBR3a ASBR3b P3b/nh ASBR3b P3a/nh ASBR3a P3a P3b

  17. BGP Diverse Paths + BGP Best External P3a/nh ASBR3a P1/nh ASBR1 PE4 • RRs and RRs’ are same RRs • RR1, RR1’ & RR2, RR2’ are in different • clusters • They are configured to calculate and • advertisediversepath to it’s clients on a • per neighbor basis • No diverse session between RRs • Best External enabled between RRs • They can do it on a per AFI/SAFI basis • Same IGP metric as best RRs • P3a overall best, P1 & P3b second best/ • diverse • RR1 and RR1’ got 2 paths • RR2 and RR2’ got 4 paths • Network still has path diversity • Single session between RRs P3a/nh ASBR3a RR1 P3a, P1 P3b/nh ASBR3b RR1’ P2 ASBR2 P3a/nh ASBR3a P1 ASBR1 P3a, P3b, P1, P2 RR2 PE2 RR2’ P3a/nh ASBR3a P3b/nh ASBR3b PE1 P3a/nh ASBR3a P1/nh ASBR1 ASBR3a ASBR3b P3b/nh ASBR3b P3a/nh ASBR3a P3a P3b

  18. Acknowledgements Special Thanks to: Randy Bush Robert Raszuk Chris Cassar SatishMynam Selma Yilmaz

  19. Questions?

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