A method (500), a system and a gateway (400) for communicating between hosts in private networks having IPv4 address spaces are disclosed. One or more DNS query messages for resolving resource records are transmitted (502) from a first private network for a remote host in a second private network. One or more DNS replies comprising a private IPv4 address for the remote host are received (504). If the one or more DNS replies comprise a synthesized IPv6 address, the IPv6 address is extracted from the replies and a peer IPv4 address in the first network is allocated for the remote host (508). The IPv6 address comprises a global IPv6 prefix and the private IPv4 address for the remote host. The peer IPv4 address is associated with an extracted IPv6 address for the remote host. The remote host is addressed using the IPv6 address for transmission of IPv4 packets from the first network addressed using the peer IPv4 address (510). The system comprises an application-level gateway of a domain name system (DNS-ALG), a virtual table, and a translator. The gateway comprises the foregoing system and a domain name system (DNS) server.