Bridging ethernet over Wi-Fi?

[Bill McGonigle]

How much "ethernet" on the bridge is working?  I happened to run across
this topic yesterday where it would have been really handy to bridge a
VLAN trunk across a wifi bridge, but almost everything that says that
it's "layer 2 transparent" is really just doing ARP proxy/masquerading
of a sort, which works OK for stuff that happens to fit into WiFi
framing but not other stuff.

To do real layer 2 bridging seems to require doing L2 over L3 (L2TPv3,
EoIP, VPLS, or eoMPLS) but that requires a cooperating endpoint, which
you don't have, so it can't be that.  Aside: when I get a chance I'd
like to get a config worked out to have an easily deployable L2TPv3
bridge on a pair of openwrt boxes, for when the next thing breaks.

-Bill


On 11/13/2015 11:39 AM, Joshua Judson Rosen wrote:
> I've noticed that VirtualBox and some other VM packages include
> functionality to bridge in-VM network interfaces onto the external
> network through a network interface on the host machine. I get how this works
> for ethernet, but it seems like they make it work for Wi-Fi, too;
> given that Wi-Fi frames don't actually carry enough information to
> to do bridging at the station (client) end, how the heck does this
> actually work?
> 
> The only technique with which I'm really familiar, for bridging ethernet
> through an 802.11(b|a|g|n) client interface, involves running the
> radio in a non-standard 4-address mode, which requires support
> on the AP at the other end of the wireless link; I'm fairly certain
> that's not what the VM systems are doing, because they appear to
> work with bog standard APs. So what _are_ they doing? Creating
> a second (hidden?) interface on VM host with identical MAC address
> to the interface inside the VM, and mirroring traffic between them?
> Faking it by sniffing and relaying packets at layer 3? Something else?
> Maybe something about this actually did get into a companion IEEE
> standard that I'm not familiar with?
> 


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Bill McGonigle, Owner
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