Cisco IOS NAT Port Forwarding

Lessons Discussion
3

Hi Boris,

You need extendable if you map an inside address to multiple outside IP addresses, like this:

ip nat inside source static 192.168.1.1 1.2.3.4 extendable
ip nat inside source static 192.168.1.1 5.6.7.8 extendable

Where 192.168.1.1 is the inside address and 1.2.3.5 / 5.6.7.8 are outside addresses. Cisco IOS will add the keyword automatically.

You also need it for port forwarding where you use the same inside and outside addresses for different port numbers:

ip nat inside source static tcp 192.168.1.1 80 1.2.3.4 80 extendable
ip nat inside source static tcp 192.168.1.1 443 1.2.3.4 443 extendable
ip nat inside source static tcp 192.168.1.2 22 1.2.3.4 22 extendable

I believe IOS always adds it automatically for you so you can’t configure it without.

Rene

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