I'm confused about NAT & PAT

[AlanSak]

I always thought NAT was used to translate private network addresses to public. On a simple lan, with a low end firewall (Sonic, Servgate...) you simply "Activate" NAT. So one of my questions would be, when you activate NAT, does it simply use the one public address assigned to it and translate all outgoing data to use this IP address- so it's actually PAT?? With Cisco, on a pix 501 box, NAT seems to require you to create an address pool of public addresses for each private ip address you are using. And this address pool would have a 1:1 correspondence with all private addresses within your lan- that is to say each private ip address has an available public address. This seems to defeat the purpose. And maybe this is where PAT comes in. My understanding is that PAT will actually translate all private (or public) ip addresses behind the firewall to a single public IP address. Is this correct?? Are the low end firewalls simply using PAT rather than NAT??
Can somebody please help me understand this issue. I'd really appreciate it.

 

[oj88]

Check this out:

http://www.cisco.com/en/US/partner/tech/tk648/tk361/technologies_q_and_a_item09186a00800e523b.shtml

Orlando Palomar Jr
CCIE# 11206, CCNP
CIPT Operations Specialist
Phil-Data Business Systems, Inc.

 

[AlanSak]

I'm not even a ccna yet.. Your page required a login, which I don't even have....
thanks though,

 

[adam108]

PAT and NAT are both Address Translations. Port Address translation uses a single public address to represent multiple hosts. This allows many machines to connect to the Internet using only 1 IP address. While this can be useful if browsing is the main goal for your users. However, if you want to host servers on your network you will need (or at the very least want to) allocate static public IP addresses to the servers. In this instance, NAT is a much simpler and more elegant solution.
Your simpler firewalls most likely implement PAT using the IP address of the public interface by default. In the world of Cisco, you can implement PAT or NAT or PAT behind a public interface depending upon the demands of the situation and the availability of public IPs.