I’m losing my mind over a home LAN problem, so here’s the gory bits to help me know if I’ve properly defined the problem.

My current LAN topology is roughly this:

ISP access point, no DHCP –> fixed IP DSL modem, bridged –> 5-port 10/100 Ethernet switch –> 2 fixed-IP desktop units, 1 fixed-IP Airport acting as DHCP for both wired and wireless network, 1 DHCP IP desktop unit.

The desktop DHCP box picks up the Airport IPs just fine and everything in the Airport cloud behaves properly, which allows all the client machines to use a printer made available via an Airport Express unit.

I have run a 50-foot ethernet cable from the point of entry / modem / switch up through the floor to the center of the building on the top floor where the Airport sits, giving housewide coverage. What I need to do is add another 10/100 hub or switch in that location to allow me to add more top-floor cabled devices to the LAN.

I have successfully inserted three 10/100 hubs into the network in the following topology:

5-port 10/100 switch -> additional n-port 10/100 hub device -> Airport

This works so long as the in port on the additional device is in uplink mode or connected to the first router via crossover cable. The Airport, in this configuration, remains connected to the second hub by the long cable.

So far so good.

When I tote the new hubs upstairs and add the hub to the LAN via the long cable, the hubs report linkstate. However, when I plug the Airport into an available port, the hubs do not report good linkstate to the Airport, all the Airport client devices, wired and wireless, lose connectivity.

As far as I can tell, the only change in the topology is that in the first instance, the cable out from the first hub into the uplink port on the second hub is about 4 feet long, and the cable out from the second hub to the Airport is fifty feet long. In the second case, this is reversed, such that the cable out from the first hub is fifty feet and the cable out from the second hub is about four feet. It’s my understanding that the rated length for the hubs and most similar devices is 100 meters. I just do not get what is going on.

One thought on “Network Cable Madness

  1. If you have a link light between the two hubs but you don’t get a new link light when you plug the airport into the second hub, my first guess would be that you need to use either a crossover or a straight cable to connect the airport to the second hub, whichever is the type you’re not using now. It could be that the switch can auto-sense crossover cables and the hub can’t.

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