A comedy of wireless bridges

Posted on Aug 18, 2004

In a previous entry I mentioned buying a Netgear WGE101, which is sold as an 802.11g wireless bridge. After using it for a couple of days I connected my Cisco 7960 phone and HP OfficeJet d125xi printer to the switch connected to the WGE101. This seemed okay - I could print and the phone registered with my Asterisk machine. It all seemed fine.

Later that same day I had to interview someone by phone. About three minutes into the call I stopped being able to hear him. Figuring that the call had dropped I just hung up and dialed again. The chap at the other end said that he could still hear my while I was saying “Hello, hello?”, but I couldn’t hear him. Three minutes later, it happened again. It was getting a bit embarrassing, so I gave up with the IP phone and switched to my mobile. From that point onward, every time I used the phone the call would last about three minutes, then I’d lose sound. Very frustrating. Asterisk is free software and I didn’t finish the configuration yet, so I decided that it must just be my own fault.

Then printing stopped working from some machines. Stuff would sit in the print queue on the client for ages and then, for no obvious reason, would start to print.

In trying to figure out what was going wrong, I looked at the ARP table on my fileserver. Wow - three remote IP address with the same MAC address! That didn’t seem right, particularly given that they were my printer, workstation and phone.

After some more delving I’ve come to the conclusion that the WGE101 isn’t a wireless bridge at all. It’s really something more like a layer 2 NAT device. If you have more than one computer hidden behind it then, as far as the network connected to the access point is concerned, they all share a MAC address. Exactly how the de-multiplexing works is a puzzle. Perhaps the key observation is that it doesn’t work well enough :-)

Whilst chatting on #snt about this, I wondered if 802.11b or g actually supported bridging. Bill said that it does exist, but that it requires a different over-air frame format (involving either three or four MAC addresses rather than two), and that he wouldn’t be surprised if people didn’t implement it correctly.

Armed with this I went looking. It seems as though the Netgear WG602v2 could do the right thing, as well as the Linksys WAP54G and the D-link DWP-2100AP. They all include wireless bridging in the specification and the documentation includes details of connecting two wired segments together. Great!

Simply didn’t argue about taking the WGE101 back, which was a surprise, so I ordered a pair of WAP54G from them at the same time. Earlier today a courier arrived to collect the WGE101 and drop off the WAP54Gs. Except that they left a pair of Linksys BEFW114S4 instead.

As an aside, I ordered a pair because all of the documentation I can find indicates that wireless bridging only works between particular sets of devices.

Back on the phone to customer service. Sure, they’ll take the stuff back, but they can’t simply replace them with WAP54Gs - I have to get a refund and re-order. Sigh. That would be another day wasted.

Jeremy (no URL known) suggested looking at RL Supplies, given that they are in Watford. I could drive round there and pick some stuff up. Prices look reasonable, so I’m off in the car. Except, they don’t have any WAP54Gs when I get there, despite what the computer says. They have D-link DWP-2000AP+ though, so I buy a couple of those.

Back home, crack open one of the boxes, plug it in, fire up Mozilla to configure it. No joy. Hunting around the web a bit it turns out that Internet Explorer is required. Yuck. Switch to the Mac. Still no joy - actually you need Internet Explorer on Microsoft Windows. I can probably dig one of those up, but who needs the hassle. Off they go back to the shop.

So, a couple of days and a lot of cellophane wrapping later, still nothing works. Stopping into PC World on the way past, where a WAP54G cost £99.99 (rather than the £50 everyone else wants) didn’t help. I’ll just wait (and wait, and wait…).