What reasons will cause the BGP connection down after the peer is established.

Created: Apr 5, 2016 14:22:25Latest reply: Apr 5, 2016 23:51:23 1142 1 0 0

What reasons will cause the BGP connection down after the peer is established.

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bellabella  Visitor   Created Apr 5, 2016 23:51:23 Helpful(0) Helpful(0)

The normal reasons are as follow:
1) After BGP peer established, during hold-time the keep-alive massage can’t be received, error code 4/0.
2) Receiving illegal update massage cause BGP disconnected for security consideration. BGP automatically disconnect the peer and print error message.
3) MTU problem, routers may use some special chip or manually define a MTU which cause the massages are encapsulated many times then dropped by BGP.
4) If MTU and QOS are not appropriately configured, the large update packets may be dropped caused by TCP re-transmission. When many update massages are re-transmitted, keep-alive massage maybe suppressed, making BGP consider the peer as down.
5) The network congestion may cause the keep-alive massage lost, the peer status will change repeatedly, and in addition if the BGP peer is found by IGP routing, the network congestion may cause the IGP routes lost then the BGP peer will be down.
6) Some other reasons cause TCP179 port can’t be used.
Of course BGP support many operations, so many reasons will cause BGP session reset:
1) Peer close the session, for example BGP peer configure command “ignore”
2) Configure the routes limitation (peer x.x.x.x route-limit), when the routes number exceeds the peer will be down; different device has different values.
3) Remote peer AS changes.
4) Route-reflect client configuration changes.
5) Peer group’s policy and capacity changes
6) Configure or modify the BGP router-id
7) BGP confederation is configured or removed; “confederation nonstandard” command can also cause this.
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