Docker Cookbook

76 | Chapter 3: Docker Networking

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Figure 3-1. Network diagram of single Docker host
After connecting to the host, if you list the network links, you will see the loopback
device, an 
eth0
interface, and the 
docker0
bridge, as depicted in the diagram. Docker
starts when the machine is booted and automatically creates a bridge and assigns a
subnet to it:
$ ip -d link show
1: lo: mtu 65536 qdisc noqueue state UNKNOWN ...
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 promiscuity 0
2: eth0: mtu 1500 qdisc pfifo_fast ...
link/ether 08:00:27:98:a7:ad brd ff:ff:ff:ff:ff:ff promiscuity 0
3: docker0: mtu 1500 qdisc noqueue ...
link/ether 00:00:00:00:00:00 brd ff:ff:ff:ff:ff:ff promiscuity 0
bridge
Now let’s start a container and check its network interface:
$ docker run -ti --rm ubuntu:14.04 bash
root@4e3ffb9bc381:/# ip addr show eth0
6: eth0: mtu 1500 qdisc noqueue state UP group default
link/ether 02:42:ac:11:2a:03 brd ff:ff:ff:ff:ff:ff
inet 172.17.42.3/24 scope global eth0
...
Indeed the container has an IP (i.e., 172.17.42.3) in the 172.17.42.1/16 network. On
the host itself, a virtual interface (i.e., 
veth450b81a
in the following code) is created
and attached to the bridge. You can see this by listing the links on the Docker host
with the 
ip
tool (or 
ifconfig
) and the 
brctl
tool if you installed the 
bridge-utils
package. The 
ip
command represents a collection of utilities for controlling TCP/IP
traffic in Linux. You can find the project documentation at the 
Linux Foundation
website
.
$ ip -d link show
...