19

When running Windows I was able to bridge my wifi connect through my laptops Ethernet connection so a range of ethernet only devices could piggy back off my wifi (Raspberry Pi, Xbox etc etc). I am now trying to do the same within Ubuntu, i.e the set up would be:

Wireless Router ---> Wifi on laptop ---> bridge to Ethernet ---> Device that needs internet plugged into Ethernet port

Now I have been trying to get this working in Ubuntu using brctl

I used the below command:

sudo brctl addif br0 eth0 wlan0

And get the following error:

can't add wlan0 to bridge br0: Operation not supported

I am hoping someone can help as I refuse to believe something I can do in windows very easily can't be done in Linux.

If you need any more info do let me know. Thanks

8

This cannot be done. You cannot bridge a WiFi client connection. If you could, we wouldn't need WDS, we'd just bridge.

The problem is very simple -- an access point is prohibited by the WiFi specifaction from broadcasting traffic over the WiFi network unless something authorizes that transmission. This is largely a relic from the days when WiFi networks were very slow and had poor, if any, security.

The bridge only has a client connection to the access point. This only authorizes the access point to transmit traffic bound for the bridge. Because any machines connected to the bridge are not clients of the access point, the access point has no reason to send traffic bound for them over the WiFi link. So it will not do so.

Unfortunately, WiFi is enough like Ethernet that it's easy to expect it to act like Ethernet. But it's just different enough to bite you.

WDS configuration is a specific authorization for an access point to send traffic not bound for any of its clients. When both ends support WDS, they include the address of the bridging endpoint as well as the address of the destination, authorizing the access point to send the traffic.

You have to use something other than bridging to do this. Routing with NAT, for example. You can also use four address mode, if both ends of the WiFi link support it.

  • 3
    You can solve this problem by re-writing the mac addresses with ebtables – ccarton Oct 26 '13 at 11:24
  • I notice that one person here says you can in ubuntu..and i've done something like it in windows too.. though you say it's impossible so perhaps you can explain what the difference is between that and this. In Windows when u do this youtube.com/watch?v=96Z1_6rX5qU WiFi connected to the internet.No cable in Ethernet connector..or cable of another comp in Ethernet connector. Then Selecting WiFi adaptor and Ethernet adaptor, it bridges them, n then another computer can plug its cable in and use the Internet connection The laptop's still a WiFi client I think(and not an access point) – barlop Apr 24 '15 at 21:48
  • 1
    @DavidSchwartz If a person has a laptop with no working wireless and no network switch to plug it into for internet access, but another laptop has wireless internet access, and there's no spare wireless usb stick. Then it seems the only solution is the bridging fakery. If both laptops had a working wireless network adaptor they could both just connect to the main wireless access point, no need for extra access points and WDS.. I've used the bridging fakery when one laptop couldn't do wireless. – barlop Apr 26 '15 at 17:36
  • 1
    Incorrect. For starters, a WDS is a WiFi connection, not unlike the others. Secondly, there's these cutie-pie devices called client-bridges or media-bridges that connect up via an AP and transparently bridge 3-5 Wired jacks, which can be hubs, etc. To be sure, there's probably limitations with how those work and how many MACs they can bridge FOR, but in the end...there is a way. Hell, even Linux will let you use WDS mode as a STA if you set 4addr as a mode on the device via the iw command and the driver lets you do it. You can bridge...it's just got...provisos. – Svartalf Sep 20 '16 at 22:36
  • 1
    @DavidSchwartz : Routing? Seriously? Here's a hint. The application can have 500+ nodes in the network. Can YOU make routing gracefully work that way? "Real WDS"? Can I be assured that it will work with Cisco, Aruba, Ubiquiti, and others? If so, then yes...if not...the premise is a problem out of box. I've got it working rather nicely with the madness I'm trying for with WDS-Station mode...but will it work with something other than a hostapd or similar derived Linux device? – Svartalf Sep 29 '16 at 3:02
3

I had a similar problem with LXC, I worked around the bridging issue in wifi devices. First you need a spare ethernet device in the computer. The trick is to create a route from the ethernet device to the wifi.

In the server file, change /etc/network/interfaces, pick an unused network for your virtual hosts, i.e. 10.0.0.0. Assign one IP to your spare ethernet interface, here it is eth0, bridging it like this:

auto br0
iface br0 inet static
    address 10.0.0.1
    netmask 255.255.255.0
    bridge_ports eth0
    bridge_fd 0
    bridge_maxwait 0

Once it is done you can go the MASQUERADE way as answered by Kostyantyn here before. Those should be in rc.local or in a script that you must run on boot-up or before starting the virtual domains:

# iptables -t nat -A POSTROUTING -o wlan0 -j MASQUERADE
# echo "1" > /proc/sys/net/ipv4/ip_forward

In the virtual server configure static IPs in /etc/network/interfaces. I am using network 10.0.0.0, I will start using from .2 , when you create more virtual hosts you probably will use 3, and so on. If you have many you can consider installing a dhcp server for those. The .1 is the gateway, as configured before.

auto eth0
iface eth0 inet static
    address 10.0.0.2
    netmask 255.255.255.0
    broadcast 10.0.0.255
    gateway 10.0.0.1

Configure also a DNS server, mine was the network router, in /etc/resolv.conf:

nameserver 192.168.1.1

Hope this helps

  • This is layer 3 trickery and not really "bridging"- the moment you're using iptables, you're routing. – Svartalf Sep 21 '16 at 12:23
0

I think what you really need is not a bridge but either:

  • SNAT (if WLAN has a static IP) (see this page )

or

  • MASQUERADE (if WLAN has dynamic IP - that is, IP changes)

1) create forwarding_enable_file.sh with the following content:

#!/bin/bash
echo "1" > /proc/sys/net/ipv4/ip_forward
iptables -t nat -A POSTROUTING -o wlan0 -j MASQUERADE

2) Run the file:

sudo ./forwarding_enable_file.sh

3) on the rest of the host specify your Ubuntu box as a gateway NOTE: if some of the boxes are also running Linux you can do it with this command:

sudo ip route add default via ubuntu-ip

where ubuntu-ip should be replaced by your ubuntu-box IP address i.e. 192.168.1.10

4) try pinging some IP, i.e. 8.8.8.8 from other hosts:

ping 8.8.8.8

5) check your DNS settings by pinging some domain, i.e.:

ping slivkoed.ru

6) if step 4) works and 5) doesn't, than you have problems with your DNS settings. in such case run with root privileges:

# echo "nameserver 8.8.8.8" > /etc/resolv.conf

Run step 5) again.

More information on resolv.conf can be found here.

  • Depends on what you're needing. If you need transparent (waves hand), no, you don't want that. Seriously. You need the behavior evidenced by things like Trendnet's retired TEW640-MB media bridge (STA mode session attached to 4 Ethernet ports.). This is likely only to be had with WDS (4addr) mode operation or with ebtables MAC masquerading (which is not to be confused with what you've posted)- both of which have their own pains and problems. – Svartalf Sep 21 '16 at 12:25
-1

You need to bring down the interfaces before bridging them.

ifconfig eth0 down

ifconfig wlan0 down

  • 1
    Still get the same error with both interfaces down – Zac Powell May 20 '13 at 20:30
  • @Zac Powell are you using Network-Manager? I had some past experiences that it might interfere. In that case you can try stopping the service, and bring it back up again afterwards – Legionair May 20 '13 at 21:20
  • Yes I am, ok so i should try bringing them both down and stopping network-manager then doing the birdge and then bring everything back up? – Zac Powell May 20 '13 at 21:21
  • yes, with service network-manager stop, then do your thing, start it again with service network-manager start – Legionair May 20 '13 at 21:23
  • still not working :/ everything is shut down but still get the same error – Zac Powell May 20 '13 at 21:26
-4
sudo iw dev wlan1 set 4addr on
  • Care to explain how this solve OP's problem? – Braiam Oct 13 '13 at 2:48
  • @Braiam My answer pretty much explains why this would work if it was supported by the AP. – David Schwartz Oct 13 '13 at 3:45
  • Sadly, it doesn't work with many AP's. As for how it MIGHT solve his problem if it worked right with most AP's is that it gives the AP ability through adding an additional MAC to the number given in each 802.11 frame to relay frames for more than just the authenticated MAC. – Svartalf Sep 21 '16 at 12:28
  • From another answer: serverfault.com/a/554663/280693 – jhutar Nov 5 '16 at 21:20

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