Source IP address

[ChrisAC]

Maybe someone can help me with a little problem this time

We're installing some Cisco 1720 routers with ADSL connections at the moment. In order to use static IP ranges on the customer side we're having to use a numbered link between the atm0 card on the CPE router and the SMS (ADSL access server - Redback BRAS). So that we don't waste IP addresses on these numbered links we're using a private range. So, the fa0 on the customer router might be 213.xxx.yyy.zzz, then the atm0 card might be 10.100.50.1 and the SMS will be 10.100.50.254. The SMS then has a route to 213.xxx.yyy.zzz via 10.100.50.1 and the default route on the customer router will be via 10.100.50.254. Okay so far?

Now, this works well. We did the first install using this method this morning. The only problem is (and it's a minor gripe!!) is that when we ping out from the router the source address is 10.100.50.1 (the atm0 interface) and so you can't actually ping anything outside our network from the router. You can ping from behind the router as the source IP will always be in the live range and the SMS has a route back via the 10.100.50.1 address and the core network has a route to it via the SMS.

To get around this when testing the router we can of course use extended pings and trace routes and specify the inside address as the IP source. This works but I was just wondering is there is any command that we can put in the config so that a standard ping or trace will use the interface that we specify.

Cheers guys.

Chris.
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Chris Andrew, CCNA
chrisac@gmx.co.uk
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[wybnormal]

Try a policy route map with ICMP listed in the access list used. You would push all ICMP out a certain interface and the rest would go where ever bits go

MikeS
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"The trouble with giving up civil rights is that you never get them back"

 

[ChrisAC]

I'm not sure that a policy map is going to solve my problem! I don't want to route icmp traffic out of another interface. It's a stub network so all traffic must be routed out of the atm0 interface to the SMS. I just want the source address to appear to come from the ethernet interface on the router so that it can be routed back to.

Thanks for the reply anyway.

Chris.
************************
Chris Andrew, CCNA
chrisac@gmx.co.uk
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