Re: [SLUG] Laptop Bridge

From: Ian C. Blenke (icblenke@nks.net)
Date: Wed Sep 06 2006 - 00:25:05 EDT


Joe Brandt wrote:
> Anyone know how to set up a laptop to act as a wireless bridge? I would like
> to use my laptop at SFD as a bridge so our demos (wired network) can access
> the net trough my wireless adapter.
>

Install bridge-utils:

    # apt-get install bridge-utils

Then use brctl to setup a bridged interface:

    # brctl addbr breth0
    # brctl addif breth0 eth0
    # brctl addif breth0 wlan0

Debian users can just add bridge_port to their interfaces file and
rename the interface:

    auto install
    iface breth0 inet dhcp
        bridge_ports eth0

There are issues with bridging wifi. I've had many a hairy issue with
bridging wireless networks, and getting them to work with different
vendor hardware. Needless to say, bridging and wireless can be tricky at
times:

http://linux-net.osdl.org/index.php/Bridge#It_doesn.27t_work_with_my_Wireless_card.21

"This is a known problem, and it is not caused by the bridge code. Many
wireless cards don't allow spoofing of the source address. It is a
firmware restriction with some chipsets. You might find some information
in the bridge mailing list archives to help. "

Namely, "Doing full bridging of wireless (802.11) requires supporting WDS."

To date, my greatest success has been with WRT54G (Broadcom reference
design) hardware running DD-WRT in WDS mode with bridging. However, in
WDS mode (particularly with bridging), the network is _much_ slower than
a standard STA->AP configuration. If you want speed and don't need the
extended WDS mesh coverage, I highly suggest _not_ running WDS.

Some things, like VMWare, don't like to bridge over wireless devices.
This is something else to consider. In this case, you can just IP route
a segment and use some iptables to DNAT/SNAT to it.

If you're just using a Linux gateway to bridging to client STAtions,
brctl might work for you without incident.

Anyway, good luck, have fun, and don't be afraid to run Kismet or
tethereal on your interfaces to debug framing problems.

 - Ian C. Blenke <ian@blenke.com> http://ian.blenke.com/



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