Method and apparatus for Internet Protocol Security (IPSec) and Network Address Translation (NAT) integration is described. A client obtains a public address from a gateway for IPSec communication. A mapping table is used to form associations between a local address for the client and a destination address for a peer, an Internet Security Association and Key Management Protocol (ISAKMP) Initiator Cookie and a Security Parameters Index associated with communication between the client and the peer. Incoming and outgoing routing may be done at the gateway using the mapping table.