US Patent 9407599 Handling NAT migration in logical L3 routing

For a network controller for managing managed forwarding elements running in hosts in a network, a method for configuring a host to facilitate migration of a virtual machine (VM) from a first host to a second host is described. The method configure, in the first host, a first managed forwarding element to perform (1) a logical L3 routing processing and (2) a network address translation (NAT) processing for a VM running in the first host. The method configures the first host to automatically send NAT information to the second host when the VM migrates to the second host so that a second managed forwarding element running in the second host can perform a NAT processing for the migrated VM based on the NAT information.