FIGURE 4-16 Output of Ipconfig /all command on a container host
There are two Ethernet adapters showing on the container host system. One has an IP address on the 192.168.2.0/24 network, which is the address used for the physical network to which the container host is connected. The other adapter has the address 172.25.112.1/12, which is on the same network as the container’s address. In fact, looking back at the container’s configuration, the container host’s address is listed as the Default Gateway and DNS Server address for the container. The container host is, in essence, functioning as a router between the 172.16.0.0/12 network on which the container is located and 192.168.2.0/24, which is the physical network to which the host is connected. The host is also functioning as the DNS server for the container. If you look at another container on the same host, it has an IP address on the same network as the first container. The two containers can ping each other’s addresses, as well as those of systems outside the 172.16.0.0/12 network. This is possible because the Containers feature and Docker use network address translation (NAT) by default, to create a networking environment for the containers on the host. NAT is a routing solution in which the network packets generated by and destined for a system have their IP addresses modified, to make them appear as though the system is located on another network. When you ping a computer on the host network from a container session, the container host modifies the ping packets, substituting its own 192.169.2.43 address for the container’s
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CHAPTER 4
Implement Windows containers