It is what cisco calls IP overloading. It is where multiple off-net
addresses share a single public IP. The router keeps track of the full
socket in order to remember which off-net address gets which incoming
packets. Cisco refers to NAT as having a one-to-one relationship between
off-net and public IPs, so that every host with a private address has a
corresponding public address in the router's NAT table. This uses more
public IPs, but makes the NAT process faster since it doesn't have to read
as far into the packet as PAT does. It also allows for an off-net host to
more easily service a wide array of ports. A Cisco router will do either
PAT or NAT.
Keith Moore will tell you that you shouldn't bother with either PAT or NAT
because they both violate the end-to-end connectivity convention of the
Internet, and they break a long list of standard protocols (he will send you
the RFC that lists several), and have been an evil band-aid on the IPv4
address scarcity problem and have hindered progress by prolonging the use of
v4 and forestalled mass IPv6 implementation. Did I miss anything, Keith?
From: Peter Burggasser [mailto:p(_dot_)burggasser(_at_)uta1002(_dot_)at]
Sent: Tuesday, August 15, 2000 1:34 PM
could anyone tell me whats PAT on cisco router is ? its in conjunction
with ip domain-lookup on the router, but i didnt find anything about.
thanks for help