ISP IP and Customer IP on same router

[John McNumara]

*We have a Cisco 1921 Router (2 GigabitEthernet router interfaces)

Our ISP gave us one of their public IP addresses to communicate with their equipment, and a set of our own public IP addresses.  They want us to assign their public IP on the internet facing interface on router A, and configure our public gateway IP on the company facing interface on router A, then configure router B's internet facing IP address with an address in router A's company facing interface's subnet, ultimately performing NAT / PAT on router B.

My question is can I configure 1921 to perform all the requirements from the ISP, or do I really need two routers?

If so, how?

Thank you

[Reza Sharifi · Accepted solution]

Hi,

You can do all that with one router.  The ISP gave more IPs just in case you have redundant routers.

Your internal facing interface on the router should be doing inside nat (ip nat inside) and the external interface connecting to the ISP should doing outside nat (ip nat outside).

Have a look at this link for some config examples.

http://www.cisco.com/en/US/tech/tk648/tk361/technologies_tech_note09186a0080094e77.shtml

HTH