Clear IP BGP - Purpose

Hi Friends - Can you explain me when I have to use "clear ip bgp" command
to reset the peer relationship with BGP Neighbors.

In my understanding iBGP advertise its any route change in 0 seconds and
EBGP advertise its route change 30 Seconds. If that is the case, what is
the purpose of using "clear ip bgp" or "clear ip bgp x.y.z.w in"
(route-refresh) commands? if the change in routing is going to get updated
automatically

 Thanks in advance

 RB

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Received on Fri Jun 27 2014 - 15:48:32 ART