Configuring simple router (should be easy).

dsmithfvc · ‎08-06-2015

Hello,

I have a 2650 Cisco router I'm trying to use to bypass a useless DSL router. The DSL router has passthrough so I can assign the internet IP to a port on my 2650. The problem I have is I can't get a host on one interface to talk to hosts on the other. My current attept looks like the following:

Host (2650 provides DHCP) 192.168.1.x 255.255.255.0 Gateway = ?

Second interface Internet IP - DSL gateway is my last resort.

DSL router is configured for passthrough.

The router can ping the internet 8.8.8.8 and appears the second interface works.

The host can ping the Internet IP but not the gateway the router can ping. I've tried the following dhcp configured default gateways on my host:

192.168.1.1 (First interface IP)

Internet (second interface IP)

Internet Gateway (I'm sure this is wrong.)

Before I was trying this without passthrough and same problem - First Attempt:

0/0 - 192.168.1.1 255.255.255.0

0/1 - 192.168.0.1 255.255.255.0

Internet router - 192.168.0.254 plugged into 0/1

Again the hosts (dchp 192.168.1.7) could ping both interfaces and the 2650 always pings everything.

Routes I tried 192.168.1.1, 192.168.0.1, 192.168.0.254. I tried static routes like 192.168.1.0 255.255.255.0 192.168.0.1 and last known resort.

Is there something obvious I keep missing in these configurations? Should the gateway of my host be 192.168.1.1 since it's on the same subnet? Even though I can ping the other subnet whether internet IP or 1st interface. I've spent hours trying everything and I'm not really sure what else to try or how to even troubleshoot from here. It just seems like a host one side never talks to hosts on the other even though it can see both interfaces.

Peter Paluch · ‎08-06-2015

Hi,

Is it perhaps possible for you to post the entire configuration of the 2650 router? It would help us understand how you have set it up so far. In other words, please post the outputs of these commands:

show running-config
show ip interface brief
show ip route

Also, what exactly does it mean that the DSL router is in the passthrough mode? Does it mean it acts as a bridge instead of a router? It is very important to understand exactly what the DSL router does right now, because if it's truly bridging then we would most probably need to star a PPPoE client on your 2650. Or is the DSL router doing some kind of NAT, forwarding the public IP address on the outside to some private address on the link between the 2650 and the DSL router? What is the exact vendor and type of the DSL router, anyway?

Should the gateway of my host be 192.168.1.1 since it's on the same subnet?

For your hosts, the gateway should be the IP address of 2650 on the same subnet with them. So if your internal hosts are on 192.168.1.0/24, and the 2650 is configured with 192.168.1.1, then the hosts should be using 192.168.1.1 as their gateway.

Best regards,
Peter