DNS, FTP and ICMP Support

NAT works with DNS by having the DNS Application Layer Gateway (ALG) translate an address that appears in a Domain Name System response to a name or inverse lookup.

NAT works with FTP by having the FTP ALG translate the FTP control payload. Both FTP PORT CMD packets and 227 Passive Response packets, containing IP address information within the data portion, are supported. The FTP control port is configurable. NAT also supports the FTP extended modes as defined in RFC2428.

The NAT implementation also supports translation of the IP address embedded in the data portion of the following types of ICMP error message: destination unreachable (type3), source quench (type4), redirect (type5), time exceeded (type 11) and parameter problem (type 12). NAT also supports an ALG for ICMP echo request/reply messages when they are forwarded via an overloaded (port-NATed) list rule.