Port Address Translation (PAT) maps a single global IP address to many local addresses. PAT extends the range of available outside addresses at your site by dynamically assigning unique port numbers to the outside address as a connection is requested. A single IP addresses has up to 65,535 ports that are available for making connections. For PAT, the port number uniquely identifies each connection.
When we add a global pool the last global command should always be a pat address in case the pool is exhausted
I had replied to this message yesterday but looks like, it got lost somehow..anyways, here's my answer again:
You second point above (which talks about using hash value) is wrong. The first one is better and correct but let me give you some more details about this whole process:
The firewall, when translating port for NAT overload (or PAT), splits the available ports into three pools:
If a packet inside you network comes into the Firewall destined for the Internet, and if
source port falls into one of those pools, the PIX will translate it to another port in
that pool. When the Firewall first starts translating addresses, it starts with the lowest port number in each pool. That means the first packet sourced internally from a high port will get sent on the Internet with a new source port of 1024. The next high port translation will go out with a source port of 1025, so on and so forth.
Table of ContentsIntroductionVersion HistoryPossible Future
UpdatesDocuments PurposeNAT Operation in ASA 8.3+ SectionsRule Types
Network Object NATTwice NAT / Manual NATRule Types used per SectionNAT
Types used with Twice NAT / Manual NAT and Network Obje...
Table of Contents Introduction:This document describes details on how
NAT-T works. Background: ESP encrypts all critical information,
encapsulating the entire inner TCP/UDP datagram within an ESP header.
ESP is an IP protocol in the same sense that TCP an...