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Chris 07-16-2009 03:05 AM

How to enable a stable BGP network?
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According to the topology above, configure R1-R4 with BGP routing, so that1. R3 and R4 are in AS 11, R1 and R2 are in AS 111.
2. Peering relationship is established as shown: blue arrow means iBGP, red arrow means eBGP.
3. Each BGP router should start announcing routes to neighbor immediately without waiting for IGP protocol to learn of the same routes.
4. BGP is configured in a way that its peering relationship is most stable.

Chris 07-16-2009 03:22 AM

Knowledge Points
  • The source IP of BGP peering needs to be reachable from neighbor router. Use logical interface such as loopback as the source help increase the stability of BGP peering:
(config-router)#neighbor update-source Loopback 0
  • When source IP of eBGP neighbors are not directly connected , e.g for R2 & R3, the following configuration is required:
(config-router)#neighbor ebgp-multihop hop 255
  • BGP synchronization is enabled by default, which states that a BGP router will not advertise to eBGP neighbors for the routes learned from iBGP neighbors, unless those routes are also known via an IGP. To disable it, configure the following Cisco BGP subcommand:
    (config-router)#no synchronization
Verify via:
(router)#show ip bgp summary
BGP router identifier, local AS number 111
BGP table version is 6, main routing table version 6
5 network entries using 585 bytes of memory
8 path entries using 416 bytes of memory
6/4 BGP path/bestpath attribute entries using 744 bytes of memory
1 BGP AS-PATH entries using 24 bytes of memory
0 BGP route-map cache entries using 0 bytes of memory
0 BGP filter-list cache entries using 0 bytes of memory
BGP using 1769 total bytes of memory
BGP activity 6/1 prefixes, 9/1 paths, scan interval 60 secs

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd 4 111 9 9 6 0 0 00:03:15 4 4 11 11 8 6 0 0 00:03:04 3

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