BGP Backdoor Cmd - All prefixes/routes

[Cannan ilangovan]

Hello Cisco Experts,

We are trying the BGP backdoor command...but this command requires we explicitly specify the prefix/route that the router learns via BGP which should be set as backdoor route when it is also being learnt via an IGP in conditions when the IGP learnt route should be set as more preferable....

network 1.x.x.x mask 255.255.255.0 backdoor is the command...we were having a real situation where we wanted all prefixes learnt via BGP to be set as backdoor...is there a way to do this? the command "network 0.0.0.0 mask 0.0.0.0 backdoor" under BGP did not help...

Thanks in advance for your time and help !!!

[Jose Jara]

Hi,

no via backdoor, but there are other ways to do it. As the network backdoor changes the AD of eBGP to 200, You can change this for all the routes with distance command:

distance bgp 200

Or

distance 200 0.0.0.0 255.255.255.255 1

access-list 1 permit 0.0.0.0 255.255.255.255

Hope this helps,

Jose

[Cannan ilangovan]

Thanks Jose....in-fact, that was the command we used in our Prod network (although Cisco Docs recommend not to use it ;-) )...however we used the other flavor of this "distance...." command (distance )

the only caveat of the "distance...." command is that we have to hard reset the BGP Peers...else this command will NOT work... which is very much a Big NO-NO in a Prod network where we have multiple BGP peers...

however, the "network....backdoor" command does NOT require a hard reset (tested this in GNS3... )...so, i think Cisco may take a look at including this command to do a "catch all"...

[Jose Jara]

Cannan,

a hard reset is not necessary, as changing the AD affects only locally. The backdoor command clears the route from the route table automatically for the change of the AD, so you can achieve the same behavior with distance command and clearing the routes manually:

clear ip route -prefix- or clear ip route *.

Hope this helps,

Jose.