Cisco NAT for IPv4
Port Forwarding
Port forwarding is a static NAT translation with a specified TCP or UDP port number.
ip nat inside source {static {tcp | udp} local-ip local-port global-ip global-port} [extendable]
interface s0/0/0
ip nat outside
interface fa0/0
ip nat inside
- extendable - option applied automatically, allows the user to configure several ambiguous static translations, where ambiguous translations are translations with the same local or global address. It allows the router to extend the translations to more than one port if necessary
NAT overload
A PAT-enabled router maintains a table that consists of a mapping of inside local IP addresses and TCP/UDP port numbers to outside local addresses and TCP/UDP port numbers. When traffic returns to the router from the public network, the router would compare the destination port to the PAT mapping table to determine to which inside host the traffic should be sent.