Thursday, October 15, 2020

BGP unsupported or mal-formatted message


If you receive an error below, the BGP relationship still might work ok. The solution is to disable the negotiation capabilities. 

BGP-4-MSGDUMP  unsupported or mal-formatted message received from x.x.x.x:
FFFF FFFF FFFF FFFF FFFF FFFF FFFF FFFF 002D 0104 95B0 00B4 7CC3 263B 1002 0E02
0041 0400 0095 B001 0400 0100 01

Additionally, this message can be decoded in order to discover if it is a BGP open message (contact the Cisco Technical Assistance Center). It also lists the capabilities for which negotiation was attempted. The capabilities this message attempted to negotiate are:

  • Route Refresh Capability
  • 4-byte AS Capability
  • Multi-Protocol Capability


The BGP is established after negotiation of the specifed capability on R1 (the router that supports the capability) is disabled. This is done with hidden commands in the BGP process.

In order to turn off all capability negotiation, enter this command:

neighbor x.x.x.x dont-capability-negotiate

In order to disable negotiation for certain capabilities, enter these commands:

neighbor x.x.x.x dont-capability-negotiate four-byte-as
neighbor x.x.x.x dont-capability-negotiate enhanced-refresh

Wednesday, October 14, 2020