NAT versus PAT

[b.withrow]

I am looking for a really good explanation and sample of PAT and NAT. It seems that the two acronyms are interchanged fairly often.

[nkhawaja]

PAT is for single external IP address, mapping to multiple internal IP addresses.

Logially one IP can be used for PATting 65535 internal IPs. (as the numbers of ports available).

NAT is a one to one translation.

Thanks

Nadeem

[mostiguy]

Basically, what Nadeem said but with this one bit of real world advice:

For every 10 people who say they are doing NAT, there is actually one person doing NAT. The other 9, have one legitimate ip address (i.e., on a cable or dsl line), and are thus in fact doing PAT.

So, when people say they are doing NAT, you only roughly know what they generally mean, as often they are doing PAT. When someone says they are doing PAT, they probably mean it.

[b.withrow]

Thanks for the reply. So, if I have 3 internal hosts connected to the 'inside' of a routerwhich routes to the internet. Would those devices be nat'd at the router or pat'd? Because some people describe it as NAT and that's what confuses me. Could you send me a link with some examples?

[mostiguy · Accepted solution]

http://www.cisco.com/en/US/customer/products/hw/vpndevc/ps2030/products_tech_note09186a00800b6e1a.shtml

should give you an idea as how the pix does it.

if your example, it totally depends on the configuration, but if you only have 1 legit external ip, you have to configure pat, as you do not have enough addresses to do nat

[nkhawaja · Accepted solution]

Another link

http://www.cisco.com/warp/public/556/nat-cisco.shtml