Problem with BGP backdoor

[nick-moore]

Good evening.  I am working on a bgp routing issue and decided that using the backdoor switch to make my router prefer my eigrp route over bgp would make routing this particular set of networks more efficient.  So, here is the problem:  I am advertising vpn client routes from my firewall at the time they connect.  These are 192.168.251.x /32 routes.  This works very well.  However, in this one site, I need to force the eigrp route to be chosen over bgp.  My config looks like this:

router bgp 65017

bgp log-neighbor-changes

timers bgp 15 45

neighbor 10.x.x.x remote-as 1850

address-family ipv4

 network 10.x.x.x mask 255.255.252.0

 network 192.168.251.0 mask 255.255.255.0 backdoor

 neighbor 10.x.x.x activate

 etc.

This does not work.  The 192.168.251.x /32 route remains ebgp with an ad of 20.

When I change the network statement to: network 192.168.251.134 255.255.255.255 backdoor, it DOES work.  The eigrp ex route is added to the routing table with the ad of 170.

So, is there a way to fix this without adding 255 network...backdoor statements?  I've tried configuring route-maps in combination with the network....backdoor statement, but no luck.

The issue is obviously related to matching the prefix and mask, but this puzzle should have a solution.  Any ideas?

[nick-moore]

I'm already modifying the ad for some other internal eigrp routes, so I'm familiar with that method. However, these are external eigrp routes and you cannot modify the external eigrp ad with the distance command. I have 8 sites exchanging routes via the single eigrp process so I don't want to modify the default ad for the protocol.

[Georg Pauwen]

Hello,

this is what I mean:

router eigrp 1
redistribute eigrp 2
!
router eigrp 2
distance eigrp 19 19
!
router bgp 1
redistribute eigrp 1
!
R1#sh ip route
192.168.251.0/32 is subnetted, 1 subnets
D 192.168.251.101
[19/130816] via 192.168.12.2, 00:03:29, GigabitEthernet0/0
!
R1#sh ip eigrp topology
EIGRP-IPv4 Topology Table for AS(1)/ID(1.1.1.1)
P 192.168.251.101/32, 1 successors, FD is 130816
via Redistributed (130816/0)
EIGRP-IPv4 Topology Table for AS(2)/ID(1.1.1.1)
P 192.168.251.101/32, 1 successors, FD is 130816
via 192.168.12.2 (130816/128256), GigabitEthernet0/0

[paul driver]

All you need to do is aggregate the ip range in bgp!’

[paul driver]

Hello
Something I find most times I have done this and it didn’t work is when I forgot the golden rule

You should state the network that is advertised you in the Network/Backdoor command  and NOT the network your local rtr is advertising!