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BGP neighbor adjacency goes down when an ACL is applied

Core Issue

The most common reason for this problem is that the ports used by Border Gateway Protocol (BGP) are not permitted through the Access Control List (ACL). BGP uses unicast Transmission Control Protocol (TCP) packets on port 179 to communicate with its peers.

Resolution

Permit TCP port 179 through the ACL.

Whenever you are applying an in-bound ACL on an interface, ensure that routing updates are not filtered out.

For more information and a sample configuration, refer to the Permit Routing Updates section of Configuring Commonly Used IP ACLs.


Type of Route Missing from Routing Table

All routes / All routes from specific neighbor

Valid Route to BGP Next Hop

Valid route to next hop exists

What Can You Ping

Default gateway can ping destination

show ip bgp neighbors {neighbor  address}

State is active

Version history
Revision #:
1 of 1
Last update:
‎06-22-2009 05:34 PM
Updated by:
 
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