Help with remote network router config

Hello people,

I need help getting hosts on my network to be able to access the internet via the following scenario:

Network A -- Router A -- Network B --- Router B --- internet

Routers A and B are Cisco 1841 modular routers (similar to 1700 and

2600 series).

Router A is connected to Router B via serial link (X.21) Router B is connected to the internet via DSL WIC on dialer interface

Router A is the new router to the scenario to connect networks A and B together.

Hosts on network A can ping hosts on Network B. Hosts on network B can ping hosts on Network A. Hosts on network B can access internet (they always could). Hosts on network A CANNOT ping any address on the internet.

Router B is configured with NAT traffic to the internet and has had no problems delivering traffic to network B.

Routers A and B are set up with RIP v1 running advertising networks A and B.

Router A was set with an "ip route network B" to ensure addresses not on networks in the routing table are delivered to Router B to pass on to the internet. I don't know if this is working as it should.

I ran a similar setup at home with a D-link router as the gateway and a Cisco 2514 where Router A is here and had no problems.

I tried using "debug ip packet" and "debu ip icmp" on Router B to see what was getting through but nothing showed up when I tried to ping a known IP on the internet.

Any help and suggestions are appreciated.


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On router B there should be a statement that selects which networks to provide NAT services, you may need to add one for the "a" network something like: ip nat inside source list 1 "or could be a pool also" access-list 1 permit access-list 1 permit

manbo wrote:

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I hadn't covered that, so I believe it's a valid point, but it does not seem to be where I'm failing. I need the right debug command to see where it is that I'm not getting through. It may be that requests to unknown networks are not going out from Router A at all but I can't seem to prove this without the right debug command. Debug all just fills too much info on the screen.


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Thanks for your patience.

I came here to post the answer to my problem, which was a NAT issue.

Router B has been working for some time and NAT was enabled on the fastethernet port (ip nat inside) and the SHDSL interface (dialer 0 : ip nat outside). Routers A and B were connected via serial interfaces and what I did NOT do is enable NAT on Rotuer B's serial interface (ip nat inside). Once I picked up on this my problem seems to have been resolved.

Using debug ip packet detail didn't help much as I could not see anything on Router A indicating my test host on Network A was trying to get through to an external host address. I did manage to establish that Router A was successfully passing requests from hosts on Network A to Router B via a traceroute command on a host on Network B. The traceroute would indicate something like this:

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Dont forget to use the command "sho ip nat trans" you'll see errors there as well as normal ops

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