[c-nsp] BGP, backdoor and route-map

Matti Saarinen mjsaarin at cc.helsinki.fi
Wed May 20 03:52:32 EDT 2009

In short, my question is has the following command any special effect in
BGP config compared to similar line without the route-map part?

network N.N.N.N mask M.M.M.M route-map foo backdoor

So, is the route-map statement just ignored silently? The IOS is
question is 12.2(18)SXF15.

Longer story leading to my question:

I have got a very ugly setup: there are Quagga boxes advertising
certaing /32 IPV4 prefixes via eBGP to few 6500s that redistribute
routes to OSPF. The 6500 don't speak iBGP with each other - the only BGP
is the eBGP to Quagga. I want to use BGP because in some cases I don't
have control over the Quagga boxes. Also I don't want to begin setting
up iBGP only for this case. The whole point of this concept is to
provide anycast service address for DNS, RADIUS etc. I don't want to
achieve load balancing just availability.

In general this setup works. The /32s are advertised. In all but one of
the 6500s the network is defined as backdoor network in BGP config so
that the same route learned via OSPF will override the one learned via
BGP. One of the servers is the preferred one and its prefix
advertisement is therefore not declared as backdoor.

Now, if I want to provide the server admins, who are also administering
the Quagga, a way to change dynamically the preferred server without any
change to Cisco config, can this be done with the current setup? I hoped
it could be done by selectively acivating the backdoor with route-maps.
I tried applying route-map to network N.N.N.N mask M.M.M.M backdoor
statement. It appeared in config but it seemed to have no effect. I
tried even to apply a route-map that would block everything but still
the prefix was declared as backdoor.


- Matti -

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