BGP route withdrawl and refresh

[tom.mcgovern]

I wish to remove one of my subnets from being advertised from my AS on my mesh of iBGP peers. After performing a "no network x.x.x.x" statement, must I then issue a "clear ip bgp * " command ? I understand that this command will reset the BGP sessions with each peer, causing all external routes from other ASs to be removed from our routing tables for up to a few minutes - thus causing loss of connectivity between our AS and the rest of the ASs. Since it is our intention to only prevent a route from being advertised outbound to our eBGP peers, I feel that the "clear ip bgp *" command could be unnecessarily disruptive.

[thisisshanky]

Hello Tom,

When you remove a network statement, you dont need, to clear the BGP table. Yes, you are right, clear ip bgp * does disrupt peerings with all neighbors.

when you give the " no network x.x.x.x" command, BGP will automatically send a withdrawn msg advertising its neighbors, that the network needs to be removed from routing/bgp table.

Some xtra info....regarding clear commands.......

YOu need to clear BGP sessions, only when you have applied a new BGP policy, like change in MED, Local pref, weight, community etc.

clear ip bgp * is a hard clearing, which resets the TCP connections totally, BGP routers go to IDLE state and starts all over again.

clear ip bgp * soft in|out could be used for a soft clearing of the BGP session. This doesnt really clear the BGP session...