System Administration Guide: Oracle Solaris Containers-Resource Management and Oracle Solaris Zones

IP Traffic Between Exclusive-IP Zones on the Same Machine

There is no internal loopback of IP packets between exclusive-IP zones. All packets are sent down to the data-link. Typically, this means that the packets are sent out on a network interface. Then, devices like Ethernet switches or IP routers can forward the packets toward their destination, which might be a different zone on the same machine as the sender.