Can someone demystify PAT for me?

Or atleast provide me with a link that does?

So many people have varying opinions about what PAT is. Some people consider it "reverse NAT", "overloaded NAT", or just describe it as something identical, in terms of function, to port forwarding. Regardless, I haven't been able to scoop out an informative explanation of PAT, and any help would be appreciated.

-Douglas

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Comments

TheNewITGuy

Well NAT being a one to one relationship, think of (dynamic) PAT as a one to many relationship. Here's a good link (and yes there is static PAT.... port forwarding)

http://www.cisco.com/en/US/docs/security/security_management/cisco_security_manager/security_manager/4.1/user/guide/NATchap.pdf

MickQ

Static NAT is a one to one mapping. One public IP to one private IP.

Dynamic NAT can be thought of as a first come first served from a pool of addresses. Think of this as at a restaurant where you come in and take any seat if there's one available. The difference between this and static is that static would have a seat pre-assigned to you and only you - bit of a waste of seating

PAT is where we have one public IP and want to run many internal private IP devices from it. Think of this as ordering a take away from a deli with the rest of us here in TE. Each person has ordered and has been given a number. There's only one window where all the food is served from. When someone's number (think port number) is called, they go up and take their food from the service window (public IP).

With PAT the router assigns a high port number for each request going out and being translated from private to public IP. This way when the reply comes back the router can look up the table, find the port number and then translate the socket (IP and port#) to send back to the correct private IP internal device.

We can also use a pool of public IP addresses for PAT but for now just think of the single address and how your home network can get out to the internet.

Darril

This thread also had some good examples and explanations: http://www.techexams.net/forums/security/88883-pat-nat-dnat-how-tell-one.html