Interesting networking problem solved

[Detonate]

As many of you know, I am the technology guy far a major non profit organization that provides free tax preparation services to the public. This year, for the first time, all three of the sites I support will be setting up their computers on a wireless network. Each site has about eight computers. The way we do this is by connecting to the sites wireless network with one of our computers which then shares it's internet connection to the other computers via a wireless router. All of the computers are running XP Pro.

My first attempt to do this ran into problems. I got the connection set up and shared on the gateway computer. But when I tried to connect with the client computers I was unable to get an IP address. Note that the router to which they are connecting has DHCP turned off, and the gateway computer with a shared connection should provide the client computers with DHCP services and an IP address.

The problem was that the routers I am using have a default gateway of 192.168.0.1 which happens to be the same gateway that XP assigns to the the wireless device on the gateway computer to provide DHCP service. It took a little research to find this out. The solution was easy, I entered the router setup page and changed the gateway to 192.168.0.2 and that solved the problem. You can't have the same IP address on two devices on the same network.

Just posting this for info. This problem not OS specific, it could happen with a Linux network also.

[SteveRiley]

Re: Interesting networking problem solved

Windows XP and Vista really want to use the subnet 192.168.0/24, and specifically the address 192.168.0.1/24 for the LAN-facing side of the ICS machine. KB 230148 explains how to change this, but it's far easier to follow the solution you found.

It's less of a problem for people who use Windows 7 ICS, because its default is 192.168.137/24, highly unlikely to collide with a typical home or small office network.

[Detonate]

Re: Interesting networking problem solved

Thanks Steve. Good to know I can change that in XP.

[SteveRiley]

Re: Interesting networking problem solved

change that in XP

Save yourself unnecessary headaches...don't do that. Several reports litter the web that the DHCP allocator service throws fits when the LAN-side ICS subnet isn't 192.168.0/24.

[Detonate]

Re: Interesting networking problem solved

I did not even try. I figured the client computers might have a hard time finding the DHCP server if I did that. And changing it in the router setup is much easier and serves the purpose.

[Detonate]

Re: Interesting networking problem solved

I thought I had the problem solved, but the networks kept crashing. I would get two or three computers hooked to the network and then when trying to connect with an additional computer, I would not be able to get an IP address. Then the whole network would crash. This thing has been driving me crazy. Today I got an error message out of nowhere when one of the connections went down about an IP conflict. Then it occurred to me that even though I had changed the gateway IP address in the router, it was no longer serving as the gateway but the new IP was still in the range of the Windows ICS DHCP server. So I believe Windows was trying to assign that same IP to one of the computers but could not. So I looked to see if I could change the IP to one outside the DHCP range of the ICS server, but alas, I could not. I tried using static IPs but the computers would connect, then after a few seconds disconnect. So I dug an old WRT54GL out of the back room where I had been keeping it as a backup and set up one of the networks with it. As you know the gateway for a WRT54GL is 192.168.1.1. A few minutes later the network was up and smoothly running. I have had it up now for and hour without any problems with three client computers hooked up. I am going to hook up some more computers and see what happens. If the system stays stable, I will be ordering some more WRT54GL's which is what I should have done in the first place.

[Snowhog]

Re: Interesting networking problem solved

I have a WRT54GL, and have been very happy with it. It's a workhorse of a router.

[SteveRiley]

Re: Interesting networking problem solved

As I look back at the earlier description of your solution, I see now why you're still having a problem. Even though you changed the IP address of the router, its north interface (192.168.0.2) was still on the same subnet -- 192.168.0/24 -- as the network behind it. I should have noticed this earlier but didn't; apologies.

Your replacement router is working not because it's a WRT54GL but because its north interface (192.168.1.1) is in a separate subnet -- 192.168.1/24. If you swap the other router back in and configure its address the same as your WRT54GL, you should see the same current proper behavior, not the goofiness you observed before.

[Detonate]

Re: Interesting networking problem solved

I already tried that Steve. The router will not let me change the address to any address except 192.168.0.XXX. When I try, the address does not change.

[SteveRiley]

Re: Interesting networking problem solved

OK, I have never encountered a wireless router with a restriction like that. I can't fathom why the manufactuer would need to limit such a basic configuration...

[Detonate]

Re: Interesting networking problem solved

Maybe I am just not smart enough to figure it out. But when I set the default gateway to an IP outside of 192.168.0.1 to 192.168.0.254 it won't save the setting and reverts to the default gateway setting. I have not tried changing the subnet mask. Maybe change it to 255.0.0.0. Would that do it?

[Snowhog]

Re: Interesting networking problem solved

My router basic network settings. They are not the factory defaults.

[SteveRiley]

Re: Interesting networking problem solved

This diagram will be helpful as you read the text below.


ISP
| <- "isp.south"
|
| <- "router.north"
router
| <- "router.south"
|
| <- "ics.north"
ICS
| <- "ics.south"
|
hosts


IP addresses are composed of two parts: the network portion and the host portion. The subnet mask differentiates between the two. With a mask of 255.255.255.0 (or the shortut /24, called CIDR notation), the first 24 bits of a 32-bit IP address represent the network; the final 8 bits represent the host. For ICS to function properly in Windows, the NICs in the sharing machine need to have addresses in separate subnets, because ICS behaves just like a router -- it is one, in fact.

Windows really really wants the ICS south side to be in 192.168.0/24; furthermore, Windows really really wants to assign the address 192.168.0.1/24 to the south-side NIC. Leave this as-is.

The north side subnet of the ICS needs to be different. Normally this happens automatically; people typically connect the north-side NIC to their ISP and allow DHCP to configure it. You've added an extra wrinkle: another router between your ICS machine and your ISP. So you have to contend with this additional subnet.

When you swapped in the WRT54GL, since it defaults 192.168.1/24 for its own south side interface, your network started working correctly. The router assigned an address from 192.168.1/24 to the north-side NIC of the ICS machine; because that's in a different subnet than what ICS automatically creates for its south side, you're all good. You will see similar behavior in any router that permits you to configure its south-side IP address.

To answer your question about 255.0.0.0 -- you could try; if that works, see if you can then change the router IP address to 10.0.0.1 and the DHCP range to 10.0.0.100..10.0.0.149. Oh -- when you first tried changing its IP address to something with a "1" in the third octet, did you also change the same octet in the DHCP range? If you didn't do this, then maybe the router's UI is blocking your change.

[Detonate]

Re: Interesting networking problem solved

I tried to change the router IP to several different IP's outside the ICS range, but it would always revert to the default IP. I had DHCP disabled in the router in order to allow ICS to be the only DHCP server. These cheap routers have been boxed up and put away now, and I have ordered replacement WRT54GL routers. I have too many things going on to try further experimentation at this time, I have to get this done ASAP as the tax preparation volunteers need to start their training next week. After things calm down and everyone is up and running, I will dig one of those routers out and play with it some more because I know there must be a solution to this problem, and I am sure that others in the tax preparation program must be having similar issues. I sent a broadcast to the tax preparation net my current solution to the problem and asked if anyone was having similar issues but I have not gotten any responses. I really appreciate you taking the time to assist, Steve. But I think we can put this on the back burner for now.