For the next meeting of the hcc pc!gg ne ... / 2008-06-15

2008-06-15 For the next meeting of the hcc pc!gg ne ... 10 years ago
For the next meeting of the hcc pc!gg netwerkgroep I wanted wired Internet access. But the location where it will be is so advanced it only has wireless Internet access. Time for a fix.

First option was a Linksys WAP54G (borrowed from work). The page in the setup where it can be configured as a wireless client already mentioned that it doesn't want to connect to other brands of networks. Too big a risk that this will not work on location.

Second option was getting a wireless - wired bridge running in Linux. The server I use for experiments with the netwerkgroep has a pci to pcmcia interface and a prism2 based pcmcia wireless card. After a bit of finding sources and getting the hostap drivers working again I set up the bridge and built a test network. First the normal iwconfig commands failed to produce results until I found that the right order is to first ifconfig wlan0 up and then iwconfig wlan0 essid 2marken.

ifconfig wlan0 up
iwconfig wlan0 essid 2marken
As a simple wireless client it works. Now to make it a bridge:
ifconfig wlan0 0 up
ifconfig eth1 0 up
brctl addbr br0
brctl addif br0 eth1
brctl addif br0 wlan0
Disabling ip on wlan0 and eth1 to take them out of normal ip routing and traffic. The bridge was working, the bridging machine was able to see the wireless network and get an IP via DHCP on the bridge interface using dhclient br0. A client machine connected to the wired connection of the bridge did not get an IP. With lots of tcpdumps running it showed that the bridge did forward the DHCP request out of the wireless interface but it never showed up on the server. Later running of another tcpdump on the same wireless network also showed no packets passing.

The one reason I can think of this happening is spanning tree doing something weird. The main ethernet switch in our house does spanning tree. Configuring that switch to force itself to be the spanning tree root also did not fix things. Or maybe the prism card does not like transmitting ethernet frames with a different source address. The Linux bridging documentation suggests this can be a problem.

Eventually I gave up and just went the standard way of masquerading from eth1 to wlan0 and setting up the standard stuff (dhcp server, nameserver). That does mean double NAT (yuck) but at least it gives connectivity.


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