using routing protocols with isdn

carl_townshend · ‎07-14-2008

Hi all, I have seen my isp's router today, there config seems to have no static routes with a higher admin distance than BGP as I would suspect, to stop the updates bringing up the line. how would they achieve this? as the line only comes up when the primary fails.

cheers

carl_townshend · ‎07-15-2008

can anyone help me with this as all?

Giuseppe Larosa · ‎07-15-2008

Hello Carl,

they are using some form of DDR Dial on Demand Routing or simply the backup command to declare that the isdn is the backup of main interface.

Then, with isdn you can define in a dialer-list what traffic is interesting (= will reset the idle timeout). Usually the idea is to use an extended ip acl where you deny the routing protocol so that BGP keepalives will not keep the ISDN line up all the time.

Look at the following link

http://www.cisco.com/en/US/docs/ios/11_3/dial/configuration/guide/dchowddr.html

Hope to help

Giuseppe