How Can One Cable Modem Work With Two Wireless Routers?
By Terry Stockdale Leave a Comment
In How to Fry a Wireless Router or Two
, I wrote about my brother's experience frying a pair of wireless modems in a lightning storm. Last week, I talked about what had happened, why it happened, and what he could do to prevent the problem in the future (this was the third set of routers, plus he lost a computer motherboard in that storm).
This week, we'll look at his network layout, and why he could not get the network to set up properly.
To summarize the situation, he has an office an a shop, with computers on his network in both locations. Some connect via wired connections (Ethernet), while others use wireless connections. His Internet cable comes into the office first.
In the past, he first used Linksys wireless routers. Then DLinks. This time, he chose Belkin wireless routers.
The incoming cable (standard cable-company RG6 coaxial cable) connects to the cable modem.
Then, the cable modem connects to the WAN (wide area network "Internet") connection on the router.
The local wired ports on the router provide connections for two wired computers. Notebooks connect via wireless connections. Finally, one wired connection on the router is used to connect an Ethernet cable that runs 250 feed to the office from the shop.
That cable was the lightning problem, as it runs outside in a conduit just a little bit underground. Effectively, he's got a 250 foot antenna looking for the electromagnetic pulse from a lightning strike. Most of us don't worry about that because our equipment is so well grounded in the house, plus the Ethernet cables we use are much shorter lines. Even if we have underground cable company lines running from their switch boxes to our houses, those lines are usually only exposed about 40 to 50 feet before they enter the dwellings.
Back to the situation. When he hooked up his replacement routers, the router at the shop immediately worked. Not so, on the router in the office. The Ethernet light and the Activity light just poounded away, blinking and blinking rapidly. But, nothing connecting to the router could get to the Internet.
If they connected a computer directly to the Ethernet cable in the office, without running it into the router first, it worked just fine. But, with the router in place, it didn't work.
The problem was the way he connected the two routers. The problem is that there is no Out Of The Box connection that will work reliably. At least one thing, usually two, has/have to be tweaked one way or another.
As one might guess, the easiest way to connect would be to connect one router's WAN connector to the cable modem, using Ethernet cable, and then use Ethernet cable to connect one of the Local Area Network (LAN) connectors on that router ot the WAN router on the other computer.
There is a problem with this setup, but it's easily solved. First, if you're using identical wireless routers, as he was, the wireless routers are both trying to use the same IP Address range and subnet mask for their local area networks.
That works fine for the first router, which is connected to cable modem. On the cable modem side, it gets an IP address on the Internet Service Provider's network - often an actual Internet address and not just a private network address. On the local area network, it assigns the IP address range specified in its setup menu. This often varies by manufacturer. In the case of Linksys, this is 192.168.1.x. In the case of the Belkin routers he bought, it was 192.168.2.x.
The problem occurs at the second router. On it's WAN side, it sees a 192.168.2.x network - but it's default setting tells it to give 192.168.2.x addresses on it's local area network side, too. In other words - it's confused. It doesn't know where to find the Internet because both networks are assigned the same addresses.
The solution was to disconnect the second router's WAN/Internet cable, connect to it via a wired computer, and tell the second router to use a different IP address range. We chose 192.168.3.x.
We hooked up the Ethernet cable to the Internet/WAN side of the router again. The router started working fine, normal light blinks for activity, no more confusion. The computers could get to the Internet just fine.
That solved the Internet connection problem. However, no computers in the office would be able to share files or printers with the shop, nor would computers in the shop be able to share with the office. That was both acceptable and intended, in this case.
It could be done; however, that would require a different configuration on the routers and connections.