BGP: 'Network xxx Mask XX Backdoor' command

[lucy.west]

i have the following situation occuring in my lab:

using 2 x 7206VXR's - both with IOS 12.2(10b)

The 7206VXR router is connected into an EIGRP network, and has eBGP peer with an 'internet router', and an eBGP peer with a second 7206VXR that is also connected into the same EIGRP cloud. The 2 7200's are in separate BGP AS's, and each has an EBGP peer with the same 'internet router'.

I am redistributing all the EIGRP routes into BGP, and advertising them out to eBGP peers, and redistributing all the BGP routes into EIGRP and advertising them out to all EIGRP neighbours.

When I apply the 'network xxxx mask xxxx backdoor' command to the BGP configuration on the 7200's, although they will prefer the internal route (i.e. the EIGRP route with AD of 90), they stop advertising this route out in their BGP updates to the internet router.

When I remove this command, they both advertise this route out to the Internet Router.

Has anyone else seen this problem, or can anyone explain why the 'network backdoor' command should stop the router from redistributing its EIGRP route into BGP, and not advertise it out to eBGP peers?

Thanks in advance

Lucy

[donewald]

Lucy,

This is normal behavior. See the following paragraph for your explaination.

A backdoor network is assigned an administrative distance of 200. The objective is to make Interior Gateway Protocol (IGP) learned routes preferred. A backdoor

network is treated as a local network, except that it is not advertised. A network that is marked as a backdoor is not sourced by the local router, but should be

learned from external neighbors. The BGP best path selection algorithm does not change when a network is configured as a backdoor.

Here's the URL... (see backdoor)

http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fiprrp_r/bgp_r/1rfbgp2.htm#xtocid15

Hope this helps,

Don