docker默認使用bridge模式，通過網橋連接到宿主機，而容器內部的ip則從網橋所在的ip段取未用的ip。這樣做一個不方便的地方在於容器內部的ip不是固定的，想要連接容器時只能通過映射到宿主機的端口，因而有很多項目使用overlay來為docker提供網絡的配置，比如Pipework、Flannel、Kubernetes、Weave、opencontrail等。
想要使用overlay來為docker配置網絡，需要首先了解下docker的網絡模式：
-
--net=bridge— The default action, that connects the container to the Docker bridge as described above. -
--net=host— Tells Docker to skip placing the container inside of a separate network stack. In essence, this choice tells Docker to not containerize the container's networking! While container processes will still be confined to their own filesystem and process list and resource limits, a quickip addrcommand will show you that, network-wise, they live “outside” in the main Docker host and have full access to its network interfaces. Note that this doesnot let the container reconfigure the host network stack — that would require--privileged=true— but it does let container processes open low-numbered ports like any other root process. It also allows the container to access local network services like D-bus. This can lead to processes in the container being able to do unexpected things like restart your computer. You should use this option with caution. -
--net=container:NAME_or_ID— Tells Docker to put this container's processes inside of the network stack that has already been created inside of another container. The new container's processes will be confined to their own filesystem and process list and resource limits, but will share the same IP address and port numbers as the first container, and processes on the two containers will be able to connect to each other over the loopback interface. -
--net=none— Tells Docker to put the container inside of its own network stack but not to take any steps to configure its network, leaving you free to build any of the custom configurations explored in the last few sections of this document.
上面這幾種方式只有--net=none才可以為docker分配固定ip，來看看如何操作。
首先，配置一個用於創建container interface的網橋，可以使用ovs，也可以使用Linux bridge，以Linux bridge為例：
br_name=docker
brctl addbr $br_name
ip addr add 192.168.33.2/24 dev $br_name ip addr del 192.168.33.2/24 dev em1 ip link set $br_name up brctl addif $br_name eth0
接着，可以啟動容器了，注意用--net=none方式啟動：
# start new container
hostname='docker.test.com' cid=$(docker run -d -i -h $hostname --net=none -t centos) pid=$(docker inspect -f '{{.State.Pid}}' $cid)
下面，為該容器配置網絡namespace，並設置固定ip：
# set up netns
mkdir -p /var/run/netns
ln -s /proc/$pid/ns/net /var/run/netns/$pid # set up bridge ip link add q$pid type veth peer name r$pid brctl addif $br_name q$pid ip link set q$pid up # set up docker interface fixed_ip='192.168.33.3/24' gateway='192.168.33.1' ip link set r$pid netns $pid ip netns exec $pid ip link set dev r$pid name eth0 ip netns exec $pid ip link set eth0 up ip netns exec $pid ip addr add $fixed_ip dev eth0 ip netns exec $pid ip route add default via 192.168.33.1
這樣，容器的網絡就配置好了，如果容器內部開啟了sshd服務，通過192.168.33.3就可以直接ssh連接到容器，非常方便。上面的步驟比較長，可以借助pipework來為容器設置固定ip（除了設置IP，還封裝了配置網關、macvlan、vlan、dhcp等功能）：
pipework docker0 be8365e3b2834 10.88.88.8/24
那么，當容器需要刪除的時候，怎么清理網絡呢，其實也很簡單：
# stop and delete container
docker stop $cid docker rm $cid # delete docker's net namespace (also delete veth pair) ip netns delete $pid
更多docker網絡的配置，可以參考官方手冊