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Ip unnumbered

I need to give a customer a static ip on router2 that is already configured in a loopback range on another router (router 1). It is on a atm interface and in the past I just used ip unnumbered loopback1 and then ip route x.x.x.x 255.255.255.255 atm2/2.2

But the loopback is actually on the other router(router 1). Could I use a ip unnumbered fastethernet command on the atm interface(router 2). Then on the router where the loopback range is actually configured I could do a ip route (his static) 255.255.255.255 (ip of router 2). I would then do a ip route (his static) 255.255.255.255 (his atm int.) Will that work?

Thanks for the help!

1 REPLY

Re: Ip unnumbered

x.x.x.0/24 routerb------------routera x.x.x.x/32

Since each of these routes has a different prefix length (subnet mask), they're considered different destinations, and they will both be installed in the routing table. Longer prefixes are always preferred over shorter ones when forwarding a packet. If they had the same mask (seen as same destination), the router would forward packets to the directed connected interface as it would have a admin distance of 0, compared to 1 for static routes. But when routerB receives a packet for x.x.x.x, it will forward it to routerA, as the routes have a different mask. I tested this before and it works.

You are lucky it's a loopback because if it were an interface, packets on that interface destinated for that host IP wouldn't get there - ANDing process would see the IP as on the local subnet and wouldn't send it to the default gateway, would arp for it (assuming proxy-arp is off).

Steve

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