1 / 8

Deterministic Route Redistribution in BGP Networks

This paper discusses the challenges of non-deterministic routing behavior in route redistribution into BGP networks and proposes a solution using administrative distance in BGP route selection.

Download Presentation

Deterministic Route Redistribution in BGP Networks

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. Deterministic Route Redistribution into BGPEnke Chen (enke@redback.com)Jenny Yuan (jenny@redback.com)

  2. Introduction • Routing protocols download routes to RIB • RIB uses the “administrative distance” to break ties between routes from different protocols, and then program the forwarding engine • BGP uses the LOCAL_PREF, AS_PATH, MED, IGP metric for route selection • Currently the two route selection algorithms are independent of each other • Non-deterministic routing behavior can occur involving route redistribution to BGP by RIB • Route redistribution into BGP is common

  3. The Problem • A is the primary connection, and B the backup. • X is statically routed on R1, R2, and redistributed into BGP. On R2, X is configured with the least preferred admin distance. R3 IBGP R1 R2 B A CUST X

  4. The Problem (cont.) • There are potentially two BGP paths for X on R2 • One received from R1 via IBGP • One locally redistributed • With the default setting, the ordering of the arrival of the paths impacts the routing behavior! • When the IBGP path arrives before the locally configured static route is redistributed into BGP • Then the IBGP path will be downloaded to RIB • RIB will select the IBGP path as the active path due to the admin distance • The locally configured static route will not be redistributed • R1, R2 and R3 will converge to the primary path

  5. The Problem (cont.) • When the locally configured static route is redistributed into the BGP before the IBGP path arrives • Then the locally redistributed path will be selected as the BGP best path (due to IGP metric) • It will then be advertised to IBGP peers • R2, and possibly R3 will use the backup path! • Additional route-specific BGP configuration can be added during route redistribution to eliminate the non-deterministic routing behavior • Expensive operationally.

  6. The Proposed Solution • Use the “admin distance” in BGP route selection • Add it as the first step in the route selection • Favor the path with a more preferred admin distance when comparing a locally redistributed path with a path received from a peer • For a locally redistributed path, its admin distance is inherited from the RIB • For a path from a peer, its admin distance is the same value as the admin distance assigned to the path for route download

  7. The Benefits • Eliminates the non-deterministic routing behavior • Avoids the extra BGP configuration • Very low computational overhead • Backward compatible

  8. Reference & Revision • draft-chen-bgp-redist-00.txt • Future revisions (as suggested by Curtis) • Expand on “admin distance” • Re-title: Use Admin Distance in BGP Route Selection

More Related