Suppose you have a two computers right next to each other. Both have Ethernet, but only one has Wi-Fi. The one with Wi-Fi is also running GNU/Linux. You want both to be connected to the Wi-Fi network. How do you go about doing this? Surely, this is easy. Linux provides this super-slick bridge interface that you can put both network interfaces in to join the two into one broadcast domain, and the Ethernet-only computer will ping out for its DHCP address and automatically configure just like so.
Not so fast. Wi-Fi doesn’t support bridging out of the box like that. Why not? Because Wi-Fi does not implement the full traditional Ethernet framing protocol. Therefore, it’s not possible to bridge across Wi-Fi in the same way it is done with Ethernet. This also explains why you may have had trouble setting up bridged networking in VirtualBox on a computer connected to the network via Wi-Fi.
If you want to get this working, you need to use one of a variety of tricks.
-
Put your computer’s Wi-fi in “access point” mode rather than “station mode.” Note that this will require other magic for a typical laptop or desktop computer that probably simply won’t be worth it or work very well.
-
Enable
4addrmode on your Wi-Fi. Note that this will not work unless both the station and the access point have support and are configured to enable it.
-
This is probably the most preferable. Use
proxyarpfrom the packageparproutedto configure ARP proxying across your Wi-Fi link. -
iptablesmasquerade magic can be used to a similar effect of creating a bridge.
See the serverfault article for full technical details on how to perform the mentioned setup methods.
I also link other pertinent information here too.
20190612/DuckDuckGo linux bridge
20190612/https://goyalankit.com/blog/linux-bridge
20190612/https://blog.elastocloud.org/2015/07/qemukvm-bridged-network-with-tap.html
20190612/DuckDuckGo ip add bridge operation not permitted
20190612/https://bbs.archlinux.org/viewtopic.php?id=154331
20190612/DuckDuckGo linux bridge wlan eth0
20190612/https://serverfault.com/questions/152363/bridging-wlan0-to-eth0
20190612/http://web.archive.org/web/20110925231256/http://kerneltrap.org/mailarchive/linux-ath5k-devel/2010/3/21/6871733
Nevertheless, one good thing that did come out of this was that I
successfully figured out how to use wpa_supplicant manually, rather
than going through NetworkManager. If you want to do anything rather
complex with your networking, generally you need to disable
NetoworkManager and configure your Wi-Fi security manually. With WEP
security, this can easily be done through iwconfig. However, WPA2
security is too complicated for such a simple-minded control system.
Hence the need for wpa_supplicant.
So, let me demo the setup and working, since my main problem with learning these kinds of technologies tends to be a lack of demoing elsewhere in documentation and on the Internet.
sudo service stop network-manager
# Don't worry about terminating wpa_supplicant, it is auto-spawned by
# NetworkManager.
sudo killall wpa_supplicant
# Now we start our own `wpa_supplicant' just like so:
touch /var/tmp/wpa-br0.conf
sudo wpa_supplicant -Dwext -iwlan0 -c /var/tmp/wpa-br0.conf \
-C /tmp/wpa-br0.sock &
# Generate your passphrase on the command line
wpa_passphrase "<SSID>"
# Enter your passphrase on stdin.
# Use `wpa_cli' to get command-line access to the daemon.
sudo wpa_cli -p /tmp/wpa-br0.sock -i wlan0
# Now we need to add a new network. Check the available networks.
scan_results
add_network
# Prints the new ID, i.e. "0"
set_network 0 ssid "<SSID>"
# Optional, the default should be okay:
set_network 0 key_mgmt WPA-PSK
# Show basic network information
list_network
# Switch it on:
select_network 0
# Enjoy, disconnect as follows:
disable_network 0
quit
# Now if you want to learn how to create a config to set yourself up
# quicker, read the man page wpa_supplicant.conf.
man wpa_supplicant.conf