Geek Network Question

[crokett]

My FIL has has AT&T DSL. ATT gave him a combo DSL/router. He bought a wireless router for when he goes to Minnesota. We set it up on his ATT connection tonight. I was expecting the router to just firewall ATT and present him with another IP address, except that didn't happen - the router became a passthru device and he got the same IP address from ATT with the router plugged in that he had with it gone. I considered that maybe the router would assign an IP address on the same subnet (192.168.1.x) as ATT does except the router management IP is a 192.168.2.x address and we couldn't even ping it with it plugged in.

Anybody heard of this? It breaks networking rules as I understand them.

[BobSch]

If I remember Routing 101, an IP of 192.16 is a non-routable (think local only) address. The address from AT&T should be a separate IP in a non-192.168 range.

[jonmulzer]

Is the subnet mask set to 255.255.255.0? Change the subnet mask to 255.255.0.0 and then set your local network to route on 192.168.2.x and see if that resolves your issues. It could be the NAT tables in the router are getting confused with the WAN and LAN sharing the same addressing scheme. It could be trying to ping to the WAN since it shares the same IP as the router.

[crokett]

Nemmermind. It may be simpler than that. I was downstairs staring at my router and it occured to me that if he plugged the modem and the laptop into LAN ports I would see that exact behavior.

Assuming that is not true, the ATT I think is router/modem combo and is definitely handing out 192.168.1.x addressess. That said, netmask 255.255.255.x is correct. With that subnet, 192.168.2.x and 192.168.1.x are on different networks. If I make the mask 255.255.0.0 then they end up on the same network.

[final_t]

The way it should be set up is:

Computer -> LAN port on the wireless -> WAN port on wireless -> CableDSL modem

LAN port on the wireless might also just be the wireless itself.

Assuming that the device is using it's default config, then that should be it. The Cable service will be assigning an ip to the WAN side of the wireless router, and the wireless router will assign a different ip (192.168.x.y) to your computer(s).

As for the possbility of both the WAN and LAN sides having the same IP - this is possible, if the device is configured to grab the computer's MAC address and pass that to the CableDSL service (MAC's are used to assign DHCP numbers).

As for breaking the rules, this seems to work ok from what I've seen. I've currently have my wireless brick daisy-chained into an existing NAT, so it's going from 192.168.0.z to 192.168.2.x to 65.44.33.y.

[rnelson0]

If you truly are getting an address from the AT&T DSL modem, the router could be in Bridge mode. Bridge mode is just that - it bridges the physical connections of two ethernet segments, basically making one long cable from the DSL modem to the desktop. I highly doubt that's the case as a lot of routers don't have that function and I am not aware of any using that as their default, but it's possible.

[jonmulzer]

Nemmermind. It may be simpler than that. I was downstairs staring at my router and it occured to me that if he plugged the modem and the laptop into LAN ports I would see that exact behavior.

Assuming that is not true, the ATT I think is router/modem combo and is definitely handing out 192.168.1.x addressess. That said, netmask 255.255.255.x is correct. With that subnet, 192.168.2.x and 192.168.1.x are on different networks. If I make the mask 255.255.0.0 then they end up on the same network.

You are correct, I did not sleep well last night and on that note I am going to bed so I can get some rest and make sure I do not hand out crappy advice in the future. Or at least try not to. I got things mixed up in my mind.

Plus, I missed the most obvious. Ockham's Razor would apply here. I am sure the others and yourself are most likely correct. TPLBKAC?