9.3 Configuring BGP  
  9.3.5 Clearing the BGP table  
When configuring BGP, changes made to an existing configuration may not appear immediately. In order to force BGP to clear its table and reset BGP sessions, use the clear ip bgp * command as follows:

Router#clear ip bgp *

The asterisk (*) is a wildcard that matches all table entries. Therefore, 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 in the following:

Router#clear ip bgp 10.0.0.0

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