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
