1 / 24

Border Gateway Protocol (BGP)

Border Gateway Protocol (BGP). Network Protocols and Standards Winter 2007-2008. Current Internet Architecture. (1999-2000). Allocated AS Numbers. BGP Routing. The de facto standard for inter-AS routing Path Vector Protocol Extension of Distance Vector Protocol

lavey
Download Presentation

Border Gateway Protocol (BGP)

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. Border Gateway Protocol (BGP) Network Protocols and Standards Winter 2007-2008 CS573: Network Protocols and Standards

  2. Current Internet Architecture (1999-2000) CS573: Network Protocols and Standards

  3. Allocated AS Numbers CS573: Network Protocols and Standards

  4. BGP Routing • The de facto standard for inter-AS routing • Path Vector Protocol • Extension of Distance Vector Protocol • Each Border Gateway broadcasts to neighbors (peers) the entire path (i.e., sequence of ASes) to the destination • Example: • X stores the following path to destination Z • Path (X, Z) = X, Y1, Y2, …, Z • Different from RIP distance vector CS573: Network Protocols and Standards

  5. BGP Routing • Now X may send this “path vector” to another border router W through BGP • A promise that I will take care of traffic for Z • Gateway W may or may not select the offered path, based on: • Cost • Policy • Additional reasons (later!) • If W selects the path advertised by X • Path (W, Z) = W, Path (X, Z) CS573: Network Protocols and Standards

  6. BGP Routing Policy • A, B, C are provider networks • X, W, Y are customers (of provider networks) • X is dual-homed: attached to two networks • X does not want to route from B via X to C • So, X should not advertise to B that a route to C exists! CS573: Network Protocols and Standards

  7. BGP Routing Policy • A advertises to B the path AW • B advertises to X the path BAW • So that X can reach W • Should B advertise to C the path BAW? • No way! B gets no “revenue” for routing CBAW since neither W nor C are B’s customers • B wants to route only to/from its customers! CS573: Network Protocols and Standards

  8. Transit versus Non-transit AS CS573: Network Protocols and Standards

  9. BGP Operation CS573: Network Protocols and Standards

  10. BGP Operation: Messages • Peers exchange BGP messages using TCP • OPEN • Opens a TCP connection to peer • Authenticates the sender • UPDATE • Advertises a new path (or withdraws old) • KEEPALIVE • Keeps connection alive in the absence of updates • Serves as ACK to an OPEN request • NOTIFICATION • Reports error in a previous message • Closes a connection CS573: Network Protocols and Standards

  11. A BGP Update Message • TIME : Tue Jun 1 00:08:03 2004 • LENGTH : 72 • TYPE : Zebra BGP • SUBTYPE : Zebra BGP Message • SOURCE_AS : 7018 • DEST_AS : 6447 • INTERFACE : 0 • SOURCE_IP : 12.0.1.63 • DEST_IP : 128.223.60.102 • MESSAGE TYPE : Update/Withdraw • WITHDRAW : • ANNOUNCE : • 64.166.88.0/24 • ATTRIBUTES : • ATTR_LEN : 29 • ORIGIN : 0 • ASPATH : 7018 701 19714 • NEXT_HOP : 12.0.1.63 • MED : N/A • LOCAL_PREF : N/A • ATOMIC_AGREG : N/A • AGGREGATOR : N/A • COMMUNITIES : 7018:5000 CS573: Network Protocols and Standards

  12. BGP Attributes CS573: Network Protocols and Standards

  13. BGP Route Selection CS573: Network Protocols and Standards

  14. BGP Route Selection CS573: Network Protocols and Standards

  15. B A D C eBGP and iBGP 18.0.0.0/8 eBGP iBGP Border router/ Egress Autonomous System (AS) Route CS573: Network Protocols and Standards

  16. Distributing Reachability Information within the AS Note: Border routers also need iBGP sessions with I internal routers CS573: Network Protocols and Standards

  17. Route Reflectors CS573: Network Protocols and Standards

  18. Problems with Route Reflectors • Problem 1 • Routers may not choose best route • Because, RR only relects its own best route • Problem 2 • RR choose their best route and make full mesh • This may result in forwarding loops • See BGPsep paper (Infocom 2006) CS573: Network Protocols and Standards

  19. 3a 3b 2a AS3 AS2 1a 2c AS1 2b eBGP session 3c 1b 1d 1c iBGP session Distributing Reachability Info to other Autonomous Systems • With eBGP session between 3a and 1c, AS3 sends prefix reachability info to AS1. • 1c can then use iBGP to distribute this new prefix reach info to all routers in AS1 • 1b can then re-advertise the new reach info to AS2 over the 1b-to-2a eBGP session • When router learns about a new prefix, it creates an entry for the prefix in its forwarding table. CS573: Network Protocols and Standards

  20. BGP Route Oscillations CS573: Network Protocols and Standards

  21. BGP Route Oscillations CS573: Network Protocols and Standards

  22. BGP Route Flap Dampening CS573: Network Protocols and Standards

  23. BGP Route Flap Dampening CS573: Network Protocols and Standards

  24. Cisco IOS Example CS573: Network Protocols and Standards

More Related