Re: Prism / Hostap Bridge Problems...

[Stephen Hemminger <shemminger@osdl.org>]

Read the FAQ 
http://bridge.sourceforge.net/faq.html
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It doesn't work with my Wireless card!
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.

Has anyone found a way to get around Wavelan not allowing anything but its own MAC address?
(answer by Michael Renzmann (mrenzmann at compulan.de))

Well, for 99% of computer users there will never be a way to get rid of this. For this function a special firmware is
needed. This firmware can be loaded into the RAM of any WaveLAN card, so it could do its job with bridging. But there is
no documentation on the interface available to the public. The only way to achieve this is to have a full version of the
hcf library which controls every function of the card and also allows accessing the card´s RAM. To get this full version
Lucent wants to know that it will be a financial win for them, also you have to sign an NDA. So be sure that you won´t
most probably get access to this peace of software until Lucent does not change its mind in this (which I doubt never
will happen).

If you urgently need to have a wireless LAN card which is able to bridge, you should use one of those having the prism
chipset onboard (manufactured by Harris Intersil). There are drivers for those cards available at www.linux-wlan.com
(which is the website from Absoval), and I found a mail that says that there is the necessary firmware and an upload
tool available for Linux to the public. If you need additional features of an access point you should also talk to
Absoval.

I still don't understand!!
(answer by Mark S. Mathews (mark at absoval.com))

Bridging Ethernet (v2 or 802.3) is predicated on the ability of a station to transmit frames with a source address (SA)
other than its own. This is possible because Ethernet uses a 'transmit and forget'/stateless transmission model.

This isn't possible with 'normal' 802.11 station cards and software because 802.11 station mode doesn't allow the
transmission of frames with 'someone else's source address. The primary reason is that 802.11 is an acknowledged
protocol. If you transmit a frame with someone else's source address, the ACK will never come back to you. The ACK will
be sent to the station whose source address you used.

There are ways to make it work (that's how I earn a living ;-), but it is not always straightforward and you probably
won't get it right without a pretty solid understanding of 802.11, it's modes, and the frame header format.