1 / 19

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

rusty
Download Presentation

BGP Diverse Paths

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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?

More Related