One-to-One NAT with different subnet on Sonicwall

Just picked up a client with a bonded T1 through Time Warner and have run into a configuration that I didn't know was possible, just wanted to find out why or how this is possible.

Firewall is a Sonicwall Pro 2040.

Their primary external IP is (changed) with a /30 subnet, with an internal NAT

There are also one-to-one NAT entries for several servers. Their external IPs are And the entries work.

Should this be possible? Is this something that the ISP has to set up to be possible? Is there a good overview of one-to-one NAT that I could read to understand what's going on?
Who is Participating?
digitapConnect With a Mentor Commented:
Go to Network > Interfaces.  Look to see if there is a secondary set of public IP address configured for the WAN interface.  Or, they have a secondary Internet connection and that will show up under Network > Interfaces.Another possiblility is the ISP has a different set of public IP addresses and they are routing those to your primary gateway (WAN interface IP address).Or, your situation sounds similar to this question:
Dave773Connect With a Mentor Commented:
It sounds like the customer owns their own address space which is getting routed through their TW connection.
If you check ARINs website, you should see that they own the addresses falling in the space. Just put one of their IPs in this tool: 
jimmyray7Connect With a Mentor Commented:
That is completely do-able.  Here is the doc on 1 to 1 NAT -
The WAN Interface will only show the primary IP and subnet.  In order to see any other networks on an interface, view the ARP entries to see if another network range has been attached to the X1 interface.  (sub interfaces, like vlans, will show on the interfaces page)
Thanks for the points!
Question has a verified solution.

Are you are experiencing a similar issue? Get a personalized answer when you ask a related question.

Have a better answer? Share it in a comment.

All Courses

From novice to tech pro — start learning today.