Re: [Bridge] Hardware requirements for bridging wired+wireless together

[Simon Barber <simon@superduper.net>]

I did write an ebtables module to work around this 802.11 3 address 
problem - it performed L2 NAT on DHCP, ARP and IP packets, so allowing 
an 802.11 client be added to a bridge. It was released under GPL about 5 
years ago (from my previous company Instant802/Devicescape), but I can't 
find the source anymore!!!

Simon


On 05/19/2010 12:20 PM, John W. Linville wrote:
> On Wed, May 19, 2010 at 10:15:35AM -0700, Umar Qureshey wrote:
>
>> What about bridging in Ad-Hoc mode?  Would that technically work?
>
> No.
>
>> I guess what I am trying to figure out is why bridging would work in WDS mode?  What is it about that mode that allows bridging to work?
>
> It has to do with the MAC-layer addressing on wireless LANs.  Wireless
> frames can use 2, 3, or 4 MAC addresses to identify the transmitter,
> receiver, sender, and destination.  For most frames and most modes,
> 3 MAC addresses are used.  The FromDS and ToDS bits in the header
> are used to allow one of the MAC address fields to specify either
> the transmitter and sender or the destination and receiver.  This is
> sufficient for non-bridged cases since the wireless station is either
> an endpoint of the communication or possibly a router (and therefore
> a Layer-2 endpoint).
>
> WDS (or 4 address) mode removes this limitation by using 4 MAC
> addresses to identify all 4 roles independently.  So, the wireless
> station is able to forward frames received off the air to the
> appropriate destination with the correct sender information intact.
>
> mac80211-based devices can have interfaces created with support for
> 4 address mode using the iw command.  For this to work, your AP has
> to be willing to accept and forward those frames appropriately --
> some do, others don't.  This is only supported for "managed" mode
> interfaces AFAIK.
>
>> If one were to try to modify the kernel code to allow MAC-level NAT, which area of the kernel code would one look at?
>
> netfilter -- I thought there was already some ebtables code to
> do this...?
>
> John