Cease Connection Collision Resolution

[Bob Greer]

Hi there,

Thanks for reading.

My company operates a few modest call centers.  We have a MPLS connections for primary voice connectivity with DMVPN over the Internet for failover.  We have a new center which opened without the DMVPN failover.  Naturally, the MPLS network hiccupped with the CCCR message.  Our provider sent this copy / paste:

We are showing that the port did change states today. The last error in the PE router is Cease (Connection Collision Resolution):
In general, it means that both peers successfully established a TCP connection, and one connection was closed. This happens from time to time and does not indicate a problem. 

If a pair of BGP speakers try to establish a BGP connection with each other simultaneously, then two parallel connections well be formed.  If the source IP address used by one of these connections is the same as the destination IP address used by the other, and the destination  IP address used by the first connection is the same as the source IP address used by the other, connection collision has occurred. In the event of connection collision, one of the connections MUST be closed.

From their chair, not a problem.  From my chair, we dropped calls.

Is there an architectural restructure or better protocol or unused feature to mitigate the possibility of this happening again?

Thanks again for reading!

Bob

[sarahr202]

Hi Bob,

We can avoid this situation by specifically identifying which BGP peer should acts as server ( i .e start listening on tcp port 179 and do not initiate TCP handshake until heard from other bgp peer) and which BGP peer should act as a client ( initiates TCP hand shakes at TCP port 179 as destination port)

This will ensure there will be only single TCP session between BGP peers

EXAMPLE:

R1--199.199.199.0/30---R2

R1;

router bgp 1

neighbor 199.199.199.2 remote-as 1 ( expect connection request from 199.199.199.2 on TCP port 179)

neighbor 199.199.199.2 transport connection-mode passive ( do not initiate  TCP hand shake with BGP peer 199.199.199.2)

Above config will instruct R1 to start listening on TCP port 179 and do not initiate TCP session for BGP i.e do not start TCP hand shake unless R2 sends TCP SYN at TCP port 179.

It will help us avoid collision you mentioned, optionally you can configure R2 as active but it is not required

R2

router bgp 1

neighbor 199.199.199.1 remote-as 1

neighbor 199.199.199.1 transport connection-mode active

NOTE:

The only thing you need to ensure service provider 's router is not configured with " neighbor X.X.X.X transport connection-mode passive

Where X.X.X.X is the IP your router 's IP being used for BGP.