How assign valid ip addresses behind a cisco router when IP unnumbered command is not applicable

[ali_ebrahimi]

Hi everybody

I am setting up a router as an Internet facing router. The outside interface is a 1Gbps interface and I cannot use IP unnumbered feature. How can I assign valid IP addresses to my firewall, servers and VPN concentrator behind the router?

Then, how can I further assign valid IP addresses to servers behind the ASA firewall?

Thank you in advance

Ali Ebrahimi 

[Peter Paluch]

Ali,

The WAN interface of your internet router must be configured with an IP address assigned to you by your internet service provider (ISP). You can not invent an IP address and place it there - it must be an IP address that is assigned by your ISP. I assume that you are accessing the public internet, and so the IP address on the WAN interface is also going to be a public (that is, not private) IP address.

To address the network behind your router that consists of a firewall, servers and VPN concentrator, you either need to request a block of public IP addresses from your ISP to use in your internal network, or you need to use NAT, in which case you can use any private IP addresses inside your network. I do not see any other way.

Considering that IPv4 addresses are scarce now, I do not suppose you will be able to get a reasonably sized public IP address range (and it might be quite expensive). Therefore, I tend to believe that NAT is probably the option you will go with.

Best regards,
Peter