BGP will be stuck with 'Connection Collision Resolution' when RE protect filter has only 'source-port' allowed in term for BGP.

It will come up after sometime, if ACX7K initiates tcp syn & not peer.

Apr 19 14:16:52.728  JTAC rpd[10501]: bgp_handle_notify:4614: NOTIFICATION received from a.b.c.d (Internal AS XXYY): code 6 (Cease) subcode 7 (Connection Collision Resolution)

set groups PROTECT_RE_GROUP interfaces lo0 unit <*> family inet filter input Protect-RE-v1.0R1
set firewall family inet filter Protect-RE-v1.0R1 term BGP-Permit from source-port bgp

Summary: 

       The behaviour is expected as per the configuration present in the ACX nodes.

       The ACX nodes have BGP-Permit rule installed on lo0 (with only ‘source-port bgp’ term).

       What the BGP-Permit rule does : drop BGP sessions initiated by other nodes.

       Due to the above rule + BGP connection collisions, it takes time for BGP to get into Established state.

       The above also explains, why configuring the BGP peer as Passive helps.

Suggestion :

           1. Configure PEER as passive.

               This is what the BGP-Permit rule expects, accept sessions initiated by ACX.

           OR

           2. Add a rule in BGP-Permit to accept dest-port as BGP.

               This will help ACX to accept BGP sessions initiated by PEER.