Hard Reset vs Soft Re-Convergence of BGP Neighbors

Here I am going to analyze the packet flow between 2 BGP neighbors for 2 types of commands.

clear ip bgp *
clear ip bgp * [in|out]

1st one is used to hard reset the BGP neighbors & the 2nd one is called a soft re-convergence. Let's find out why it is said so using a packet capture.

Packet flow of clear ip bgp *

Now let's try a soft re-convergence hitting clear ip bgp * in

clear ip bgp * out

clear ip bgp * in means asking the neighbor to resend the NLRIs and clear ip bgp* out means to resend NLRIs to neighbor.

As you can see, TCP session will be re-established when you hit clear ip bgp * but only the routing updates will be re-transmitted in soft re-convergence method. So a soft re-convergence can be used in production environments without causing a network interruption.

Note that for some configurations like changing BGP timers may need to use the hard reset command in order to be applied.

Download the packet capture from here.