-- SimonLangley - 17 Sep 2005

Wireless LTSP Clients

Using a Wireless Ethernet Bridge

Introduction

If you already operate a wireless LAN, using laptops as wireless LTSP clients is an attractive option. However, booting over the network is not as straighforward with a wireless NIC as with a wired one as few if any wireless NICs can boot off the network. If you want to boot from the network (as opposed to floppy/CD/USB disk/CF disk etc) using a PCMCIA wireless card is not an option because these will only work once the kernel has been loaded and without the wireless card, the machine won't be able to load the kernel.

The approach I successfully adopted was to connect a physically small wireless ethernet bridge to my laptop's built-in ethernet card (which does support network booting using PXE) and to fool the laptop into thinking it was on a wired LAN.

Configuration

The pre-requisites for this approach are:

• an ethernet card that supports booting over a network (required for all LTSP clients)

• a wireless bridge or access point that can operate as a bridge (a router won't work) to connect to the client's ethernet port

• a wireless bridge or access point that can operate as a bridge (a router won't work here either) to connect to the main switch or hub on your network which must be on the same subnet as your LTSP server.

Most wireless APs would be suitable to connect to the client, but the cheapest suitable devices are often marketed as "wireless ethernet bridges" and are usually advertised for connecting devices such as games consoles to a wireless network.

Most people considering this option will already have the AP connected to their wired LAN in place.

The reason you cannot use routers for either of these APs is that routers do not forward broadcast traffic (which is what DHCP requests are) to another LAN segment. The LTSP server will therefore never see DHCP requests and so the client will not boot.

First of all, you will save difficulties later on if you check that the client machine will boot as an LTSP client on a wired network. If this doesn't work nothing else will so get this set up first.

Secondly you need to set up your wireless AP. For all the wireless APs I have used this is done using a web interface from a machine directly connected to the AP. Ensure that you have correctly configured WEP/WPA/WPA2 as appropriate, that the AP is configured to operate in client mode.

If your LTSP is configured to recognise the MAC of each client's NIC, you should also configure your AP to clone the MAC of the NIC to which it is connected. If you don't do this you will need to add another entry to your dhcpd.conf file on the LTSP server with the MAC of your AP (my AP can clone the MAC so I haven't tested this but it should work).

If the client machine has an operating system installed that works on the wired network, you should test the configuration of your AP. If you plug the AP into your client machine, and then boot up, it should see the network (whether your wired ethernet port has a static or dynamic IP address). You should not need to make any configuration changes at all to the existing OS setup and this should work regardless of the OS you are using.

Testing

Once you have these two elements working, you are ready to test LTSP.

Turn the AP connected to the client machine on and wait for a minute or so (to allow the AP to associate with the AP connected to your wired network). Now turn on the client machine and if you have correctly configured everything else, your machine should boot up almost exactly as if it were connected to the wired network. The only visible difference should be the lower speed of a wireless network compared to a wired network. If your wired network is only 10Mbps and you are using an 802.11g network, you may not even notice this difference.

Have fun.