When a BGP filtering method has been changed, the BGP session may need to be cleared for the new filtering method to take effect.
Typically when a BGP policy changes, the BGP table must be processed by the router for the filtering changes to take effect.
There are two methods of clearing a BGP session, a hard reset, or a soft reset.
If the neighbouring router has a route refresh capability, a soft reset may be all that is needed.
A hard reset is carried out with the command
clear ip bgp x.x.x.x where x is your neighbours IP address. Alternatively all BGP sessions can be cleared with the command
clear ip bgp *
! Clear session with neighbour 126.96.36.199 clear ip bgp 188.8.131.52
A hard reset will tear down the entire BGP session with the neighbour, and require it to renegotiate with its neighbour to bring the session back online from the beginning.
To soft reset a session with a BGP neighbour, use the command
clear ip bgp x.x.x.x soft
! Softly clear session with neighbour 184.108.40.206 clear ip bgp 220.127.116.11 soft
Performing a soft reset only carries out a route refresh with the neighbouring router.
Resetting a specific address family
Without specifying a specific address family, all address families with that neighbour will be refreshed with a soft reset. You can reset only a specific address family with this example command
clear bgp ipv4 18.104.22.168 soft