8.3 Configuring BGP 
8.3.5 Clearing the BGP table
When configuring BGP, changes made to an existing configuration may not appear immediately. To force BGP to clear its table and reset BGP sessions, use the clear ip bgp * command. The easiest way to enter this command is as follows:

Router#clear ip bgp *

The asterisk (*) is a wildcard that matches all table entries; so all BGP routes are lost while the neighbor relationships are reset. This is expedient and very useful in a lab situation, but caution should be exercised when issuing this command on a production router. On an Internet backbone router, it may be more appropriate to use this command with a specific IP address, as shown:

Router#clear ip bgp 10.0.0.0

By specifying a particular network to clear, you prevent all BGP information from being temporarily lost.