Exploring how instances get their addresses

When a network is created and DHCP is enabled on a subnet within the network, the network is scheduled to one or more DHCP agents in the environment. A dnsmasq process is spawned in a network namespace that corresponds to the network. If a dnsmasq process already exists for the network and a new subnet is added, the existing process is updated to support the additional subnet.

Note

When DHCP is not enabled on a subnet, a dnsmasq process is not spawned. An IP address is still associated with the Neutron port that corresponds to the interface within the instance, however. Without DHCP services, it is up to the user to manually configure the IP address on the interface within the guest operating system through a console session.

Most instances rely on DHCP to obtain their associated IP addresses. DHCP goes through the following stages:

• A DHCP client sends a DHCPDISCOVER broadcast packet that requests IP information from a DHCP server.

• A DHCP server responds...