Using a BT Business Hub as a wireless bridge

8.08.00pm BST (GMT +0100) Sun 19th Oct 2008

After a cheap and sustainable way to get wireless in the house, I reused an ADSL BT wireless router that had been provided to a business and was no longer needed.

14.9.09: this article is about adding a wireless access point to an existing physical network, ie bridging from ethernet to WIFI. If you want to use it to supplement an existing wireless LAN, this article is not likely to help much. The link at the bottom of the page might help.

You'll need to get onto the web interfaces.

You may need to work through the steps below to get onto the web interface in the first place. Try http://home/managment if its your internet gateway.

Once you've found the web front end, if you go to the /managment page (yep, misspelt) you'll find lots of diagnostics and configuration options; such as static DNS, syslog forwarding etc.

[1] Give it a factory reset.

Its in the 'resets' page under 'troubleshooting' on the managment (sic) page.

[2] set it up using a DHCP client with a web browser

Plug in a laptop (or whatever) to one of the ethernet ports and it'll be issued an address on the default network for the BT device. Web administration is achieved by browsing to it.

On your laptop, find out the BT device's address with the command netstat -rn - it should be the only non-zero address in the 'gateway' column.

[3] Give the BT device a valid static network address

With DHCP enabled on the BT device, it'll assume that it provides internet access and advertise itself to those machines as the gateway. That won't work; for the purposes of having dumb wireless bridge, all the automatic features need to be disabled, and it needs to be told to use your network as well. (in my case, the purple one on my smoothwall)

"local network/advanced settings" page

"Private network" select "configure manually"

Give it a fixed IP on the LAN so it can be administered. Something not assigned already, and outside of the DHCP range. Set the subnet mask. Once set up and tested, you could tell the BT router that its IP address is anything: it'll simply provide the physical layer and then the clients will broadcast for an IP. The BT device doesn't care that they're getting valid IPs and it doesn't.

But it'd be a pain to reconfigure wireless - short of isolating it and messing around with static IPs, you'd have to isolate the BT device, to reset it factory settings every time you wanted to access the web admin page.

[4] reconfigure DHCP if required

We need to leave DHCP on for the moment. So, change it, if required, to a range on the same network as the hub, excluding the hub's address.

It'll then reset.

[5] get a new IP

You'll probably need hotplug the laptop network connection to trigger a new DHCP request.

[6] wireless

"Local Network" page. Select "Edit settings" under "Wireless Settings." On the wireless screen, set up the accesspoint as you see fit. Personally, I turn off broadcast and wep (13 character password) is the most reliable option for linux clients. Not very secure, but then I consider all wireless to be fundamentally insecure, and its firewalled from my main network.

Test it. Disconnect the laptop and connect via wireless.

[7] Disable DHCP in the local network/advanced screen
[8] Connect it to your network

The BT devices has four ethernet ports for clients: on one ethernet port is the 'purple' interface of my smoothwall firewall/router.

The purpose of this purple network is to segregate insecure wireless from far more secure hard wired ('green'). Purple has its own IP address range and is serviced with DHCP and dished out with a gateway for internet access. Traffic isn't routed to the green network. (Traffic is supposed to route from green to purple, but doesn't on my machine. Which is a pain!)

On a more conventional home setup, the router providing internet access probably doesn't have a dedicated wireless subnet. So, I'm assuming you're just connecting it onto your main LAN, so you have a switch or hub and want to provide wireless access to the existing network.

Both the BT device and your network device expect computers to be plugged in, not other network devices. So, you'll need either [a] cross-over cable [b] a 'link' socket on the device (used for daisy chaining switches/hubs) that either auto-detects the need to cross-over, or has a switch to do it, or [c] ports on your switch that auto-detect a crossed-over connection.

[9] check its all correct for Ethernet clients

Connect a DHCP client (such as a laptop) to one of the remaining three ethernet ports on the BT device. It should get an IP address from _your_ DHCP server (such as your internet router) and be able to access the internet.

[10] check its all correct for wireless clients

Should work the same way. Configure up the WIFI to connect to your new wireless gateway: it should get an IP address from your DHCP server, and its route to the internet (its gateway) be provided at the same time.

Further notes at the link below; screenshots don't match my device.

Footnote: on the managment (sic) page, under 'Advanced' / 'Configure services' there's an option to disable routing. I used this for a friend's setup, and it works a treat. However, it still tries to be an ADSL device, and will keep generating unhelpful errors until you select the right ADSL option (ie .. NOT PPPoE, etc.) that supports an ADSL device that doesn't route. I can't access my BT device from here, so can't be more specific. Try then all until it works!

Using a BT Business Hub as a wireless bridge

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