Centralized SNAT

Source NAT, or SNAT for short, is the method of changing the source address of a packet as it leaves the interface of a router. When a Neutron router is allocated an IP address from an external network using the router-gateway-set command, the IP is used in source NAT operations. The source IP of traffic from virtual machine instances to external networks will be translated as the router's address when the instances do not have 1-to-1 floating IPs configured. All routers in Neutron, whether they are standalone, HA, or distributed, support SNAT.

Note

As of the Kilo release of OpenStack, routers that handle SNAT are centralized on a single node and are not highly available. As a workaround, multiple nodes may be configured in dvr_snat mode.

Reviewing the topology

In this demonstration, the following provider and tenant networks are created:

Figure 9.20

Using the --distributed=true option, a distributed virtual router is created:

Figure 9.21

In this environment, the L3 agent on the...