Bridging wire and wireless using bridge-utils
Since Linux kerner >= 2.6.33 it is impossible to: "brctl addif br0 eth0 wlan0"
where eth0 is a wire and wlan0 is a wireless interface respectively.
But is seems that is not an implementation limitation, yet only an interface, maybe only one "if" in the code.
In fact it is not simple to bride wire and wireless due to the mac problem in the manage mode
(probably the wireless device refuses packets addressed with a different MAC than its)
So I assume that somebody decided to prohibit bridging wire and wirless
instead of non-trivialy extending bridge implementation in the kernel (just as Microsoft did).
And now when I issue "brctl addif brt0 eth0 wlan0" I get "Operation not supported".
It's a great pity that the decider hadn't taken the existing workaround into consideration:
the MAC problem can be resolved using ebtables, dhcrelay can solve a dhcp problem
and arp-scan to refresh ebtables rules.
Finally the wire-wireless bridge can work almost perfectly as an ordinary bridge.
There are a lot of opinions in internet that the workaround was effective and usuful and
there are a lot of questions how to brdige wire and wireless in a mange mode.
I'm writting to you because I've noticed something strange:
I managed to bridge wire and wireless via "brctl addif brt0 eth0 eth1" on Xubuntu/Ubuntu 12.04 and 12.10
(Note that eth1 is a wiress interface, naming convention has changed since Ubunut 12.*)
Xubuntu/Ubuntu 12.* are using Linux kernel version 3.2.* so I though that the bridging restriction was lifted.
Alas! In Xubuntu/Ubuntu 13.04 (pre-release version) the restriction still occurs
so it is unlikely that something in the kernel was changed in version 3.2.* regarding bridging.
I think that I discovered the reason why bridging works in Xubuntu/Ubuntu 12.*.
When I issue "iw eht1 info" in Xubuntu/Ubuntu 12.* I get error "nl80211 not found"
but my wirelles interface works correctly (with wpa_supplicant)
So it is simply a Xubuntu/Ubuntu 12.* bug.
Note that "iw" package was significantly upgraded against Xubuntu/Ubuntu 11.*.
The bug has been fixed in Xubuntu/Ubuntu 13.04, "iw eht1 info" works.
So it seems that the bug was a nice side-effect causing that the bridging restriction was cheated.
But how? Probably during "brctl addif brt0 eth0 wlan0" the kernel asks the wireless device
about mode in wich it is working, the bridging restriction affects manage mode but not access point mode.
For me and not only the bridging restriction is ridiculous especially as it causes that
wire-wireless bridge can not be obtained at all completely differently than in Windows 7.
In Windows 7 I click on two interaces wire and wireless and followed by "Brdge Connections" and it works!
From my point of view as a computer scientist the wire and wireless inferfaces for notebooks and etc.
should be bridged by default making one logical interface. It is stupid to keep them independent
while, nine times out of ten, the intefaces are used exclusively only as two ways to connect to a local subnet.
They hardly ever are used to connect two different subnets and making a notebook to be something like a router.
MY QUESTION IS:
Could you do something to make possible for ever to bridge wire and wireless interface on Ubuntu?
About usefulness of bridging. It has a lof of advantages but most important in my opinion are:
- I can connect fastly two notebooks or another device to my notebook (e.g.: printer, TV)
via wire in case copying a huge amount of data and both are connecteced to my subnet (and also have an access to internet)
- I can connect fastly sombedy elses's notebootk to my notebook when I want to temporarily give him
an access to my subnet and/or internet but I don't want to give him my wireless password.
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