How to do NAT

How to do NAT on Cisco 831

Q1: We have a Cisco router 831 with V12.3 and would like to map the ftp port pointing to inside computer with ip 172.16.5.2. How to do that?

A: With a static nat command:

ip nat inside source static tcp 172.16.5.2 21 <public IP> 21 extendable

interface [the outside interface]
ip nat outside

interface [the inside LAN interface]
ip nat inside

Q2: After added ip nat inside source static tcp 172.16.5.2 21 interface ethernet 21, it works. Thank you.

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