Docker on CentOS with bridge to LAN network

Question

I have a server VLAN of 10.101.10.0/24 and my Docker host is 10.101.10.31. How do I configure a bridge network on my Docker host (VM) so that all the containers can connect directly to my LAN network without having to redirect ports around on the default 172.17.0.0/16? I tried searching but all the howtos I've found so far have resulted in losing SSH session which I had to go into the VM from a console to revert the steps I did.

Accepted Answer

There's multiple ways this can be done. The two I've had most success with are routing a subnet to a docker bridge and using a custom bridge on the host LAN.

Docker Bridge, Routed Network

This has the benefit of only needing native docker tools to configure docker. It has the down side of needing to add a route to your network, which is outside of dockers remit and usually manual (or relies on the "networking team").

Enable IP forwarding

```
 /etc/sysctl.conf: net.ipv4.ip_forward = 1
 sysctl -p /etc/sysctl.conf
```

Create a docker bridge with new subnet on your VM network, say `10.101.11.0/24`

```
 docker network create routed0 --subnet 10.101.11.0/24
```

Tell the rest of the network that `10.101.11.0/24` should be routed via `10.101.10.X` where X is IP of your docker host. This is the external router/gateway/"network guy" config. On a linux gateway you could add a route with:

```
 ip route add 10.101.11.0/24 via 10.101.10.31
```

Create containers on the bridge with 10.101.11.0/24 addresses.

```
 docker run --net routed0 busybox ping 10.101.10.31
 docker run --net routed0 busybox ping 8.8.8.8
```

Then your done. Containers have routable IP addresses. If you're ok with the network side, or run something like RIP/OSPF on the network or Calico that takes care of routing then this is the cleanest solution.

Custom Bridge, Existing Network (and interface)

This has the benefit of not requiring any external network setup. The downside is the setup on the docker host is more complex. The main interface requires this bridge at boot time so it's not a native `docker network` setup. Pipework or manual container setup is required.

Using a VM can make this a little more complicated as you are running extra interfaces with extra MAC addresses over the main VM's interface which will need additional "Promiscuous" config first to allow this to work.

The permanent network config for bridged interfaces varies by distro. The following commands outline how to set the interface up and will disappear after reboot. You are going to need console access or a seperate route into your VM as you are changing the main network interface config.

Create a bridge on the host.

```
 ip link add name shared0 type bridge
 ip link set shared0 up
```

In `/etc/sysconfig/network-scripts/ifcfg-br0`

```
 DEVICE=shared0
 TYPE=Bridge
 BOOTPROTO=static
 DNS1=8.8.8.8
 GATEWAY=10.101.10.1
 IPADDR=10.101.10.31
 NETMASK=255.255.255.0
 ONBOOT=yes
```

Attach the primary interface to the bridge, usually `eth0`

```
 ip link set eth0 up
 ip link set eth0 master shared0
```

In `/etc/sysconfig/network-scripts/ifcfg-eth0`

```
 DEVICE=eth0
 ONBOOT=yes
 TYPE=Ethernet
 IPV6INIT=no
 USERCTL=no
 BRIDGE=shared0
```

Reconfigure your bridge to have `eth0`'s ip config.

```
 ip addr add dev shared0 10.101.10.31/24
 ip route add default via 10.101.10.1
```

Attach containers to bridge with `10.101.10.0/24` addresses.

```
 CONTAINERID=$(docker run -d --net=none busybox sleep 600)
 pipework shared1 $CONTAINERID 10.101.10.43/24@10.101.10.Y
```

Or use a DHCP client inside the container

```
 pipework shared1 $CONTAINERID dhclient
```

Docker macvlan network

Docker has since added a network driver called `macvlan` that can make a container appear to be directly connected to the physical network the host is on. The container is attached to a `parent` interface on the host.

```
docker network create -d macvlan \
  --subnet=10.101.10.0/24 \
  --gateway=10.101.10.1  \
  -o parent=eth0 pub_net
```

This will suffer from the same VM/softswitch problems where the network and interface will need be promiscuous with regard mac addresses.

Docker on CentOS with bridge to LAN network

Solution

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