1:1 NAT - What's "Internal IP" vs "Destination"?

  • When setting up a 1:1 mapping from an external WAN address to an internal LAN address, what is the purpose of the "Destination" field?

    If the source address is on the WAN, then to me the "Internal IP" is the destination. Having a second destination makes no sense.

    For my purposes I've left "Destination" set to "any" and the 1:1 mapping works properly. But I don't even know what I'm setting here by selecting "any" for the Destination, and I don't want this to be an attack vector by leaving it as "any" if that's not correct.

    The online NAT help is basically useless here, and doesn't explain the difference in terminology here, or what the Destination address is for vs the "Internal IP".

    pfSense version:
    2.0.2-RELEASE (amd64)
    built on Fri Dec 7 22:39:16 EST 2012
    FreeBSD 8.1-RELEASE-p13

  • On the edit screen, it has this text:

    The 1:1 mapping will only be used for connections to or from the specified destination.
    Hint: this is usually 'any'.

    If I understand that correctly, it means that if you want 1:1 NAT to work only for a particular Internet address or subnet, you could do that here.  I can't think of why you would want that, but it would basically limit who would be allowed to use this NAT.