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78 lines
2.8 KiB
Markdown
78 lines
2.8 KiB
Markdown
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<!--[metadata]>
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+++
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title = "Build your own bridge"
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description = "Learn how to build your own bridge interface"
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keywords = ["docker, bridge, docker0, network"]
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[menu.main]
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parent = "smn_networking_def"
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+++
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<![end-metadata]-->
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# Build your own bridge
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This section explains building your own bridge to replaced the Docker default
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bridge. This is a `bridge` network named `bridge` created automatically when you
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install Docker.
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> **Note**: The [Docker networks feature](../dockernetworks.md) allows you to
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create user-defined networks in addition to the default bridge network.
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You can set up your own bridge before starting Docker and use `-b BRIDGE` or
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`--bridge=BRIDGE` to tell Docker to use your bridge instead. If you already
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have Docker up and running with its default `docker0` still configured, you will
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probably want to begin by stopping the service and removing the interface:
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```
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# Stopping Docker and removing docker0
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$ sudo service docker stop
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$ sudo ip link set dev docker0 down
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$ sudo brctl delbr docker0
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$ sudo iptables -t nat -F POSTROUTING
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```
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Then, before starting the Docker service, create your own bridge and give it
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whatever configuration you want. Here we will create a simple enough bridge
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that we really could just have used the options in the previous section to
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customize `docker0`, but it will be enough to illustrate the technique.
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```
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# Create our own bridge
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$ sudo brctl addbr bridge0
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$ sudo ip addr add 192.168.5.1/24 dev bridge0
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$ sudo ip link set dev bridge0 up
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# Confirming that our bridge is up and running
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$ ip addr show bridge0
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4: bridge0: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state UP group default
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link/ether 66:38:d0:0d:76:18 brd ff:ff:ff:ff:ff:ff
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inet 192.168.5.1/24 scope global bridge0
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valid_lft forever preferred_lft forever
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# Tell Docker about it and restart (on Ubuntu)
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$ echo 'DOCKER_OPTS="-b=bridge0"' >> /etc/default/docker
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$ sudo service docker start
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# Confirming new outgoing NAT masquerade is set up
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$ sudo iptables -t nat -L -n
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...
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Chain POSTROUTING (policy ACCEPT)
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target prot opt source destination
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MASQUERADE all -- 192.168.5.0/24 0.0.0.0/0
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```
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The result should be that the Docker server starts successfully and is now
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prepared to bind containers to the new bridge. After pausing to verify the
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bridge's configuration, try creating a container -- you will see that its IP
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address is in your new IP address range, which Docker will have auto-detected.
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You can use the `brctl show` command to see Docker add and remove interfaces
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from the bridge as you start and stop containers, and can run `ip addr` and `ip
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route` inside a container to see that it has been given an address in the
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bridge's IP address range and has been told to use the Docker host's IP address
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on the bridge as its default gateway to the rest of the Internet.
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