Question: Two 2501 Routers

Hi Guys!
I have two 2501 routers hooked together with a back to back serial cable.

Router-A
e0 (DHCP from rest of home network)(192.168.1.0/24 range)
s0 172.16.1.1/24

Router-B
s1 172.16.1.2/24

On router A I've done "ip route 0.0.0.0 0.0.0.0 192.168.1.1"
On router B I've done "ip route 0.0.0.0 0.0.0.0 172.16.1.1"

I'm trying to ping the outside world from Router-B but simply cannot. I can ping everything from router-A. I can ping 172.16.1.1 from Router-B so I know the serial connection works but it's like Router-A is not routing my request.

I'm sure I'm doing something wrong and please forgive my ignorance...
Thanks guys!!!

Find more posts tagged with

SAVE $250 on Your CISCO Boot Camp — Use Code "EXAM26"

Exclusively for TechExams members for Infosec Boot Camps starting before April 30, 2026

View CISCO Boot Camps

Comments

mikej412

How is Router B connected to the outside world? Through Router A and your home network?

Does your home network router know how to route packets back to the 172.16.1.0 network? Other option would be to run NAT on Router A -- but you'd probably be doing a "double NAT" to get out to the internet -- but that should still work.

Netstudent

sounds like you are losing the ping on the return trip or your not getting out at all.. I have a feeling it has something to do wtih that default route on routerA. What else do you have on that 192.168.1.0/24 network?

As mike said, make sure you have a route to the 172.16.0.0 network on whatever else is in that ethernet network and make sure you can translate from a 172.16.1.0 to a public ip.

reeves122

Oh yes!

I actually did not set up a return route for that on router A.

On the 192.168.1.0/24 network I have a gateway at 192.168.1.1. Also have some other computers and devices. Pinging outside addresses like 166.102.58.210 from Router-A always works but never from Router-B.

At the moment, Router-B is only connected via serial to Router-A. I have not hooked up ethernet yet. My goal is to put a switch on the other end of Router-B and allow traffic to pass through both routers onto the Internet and back.

Ok so I understand the idea of creating a route on Router-A for the return trip but I'm not sure what to put in.

Netstudent

you need a route for the return trip on that 192.168.1.1 gateway. You need a route to 172.16.1.0 via RouterA's ethernet interface.

It sounds like you are doing NAT for the 192.168.1.0 network, but if you ping the internet from RouterB, the source address will be 172.16.1.0....So how are you going to translate that? See that 192.168.1.1 gateway does not know what to do with a 172.16.1.0 network. You may have to do NAT on RouterA that statically translates the 172.16.1.0 network to some 192.168.1.0 network address.

mikej412

reeves122 wrote:

I have a gateway at 192.168.1.1.

Does that 192.168.1.1 gateway have a route to the 172.16.0.0 network that points back to Router A?

reeves122

Using your advice I was able to get it working!

I went into my Linksys WRT54G page and set a static route just like this:

Dest network/mask
172.16.1.0/24

Gateway
192.168.1.132

Router-B now has no problems pinging any outside servers because my Linksys router at 192.168.1.1 now knows how to send packets back to the 172.16.1.0 network. Albeit, 192.168.1.132 is a DHCP address... but at least i'm making progress.

Pretty cool.. I have to thank you guys.. I never would have thought about that had you not said anything.

Thanks again!

Netstudent

just remember that all devices that "route" packets by destination IP need directions and data flow is a 2 way street. You need directions to get to a destination and directions on how to get back.