You have several choices, but some of the basic differences have to do with capabilities. For example, does your firewall act as a proxy server, also. Many do, some don't. Also, you have the choice of hardware or software firewalls. Hardware firewalls are usually noticeably faster, but more expensive. From my experience, I would pay the extra money for a hardware firewall. I love the PIX. A good book to read would be "Firewalls 24Seven" by Sybex. It has great explanations of the features of firewalls as well as descriptions of about 20 different popular firewalls for NT, Unix, dedicated firewalls, etc. Definitely worth the read.
Usually a solution is based on # of hosts, # of networks, speed, capabilities, security of the device and the list goes on and on. you might want to check out www.securehq.org. They review everything security and might give you some better insight.
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...
[toc:faq]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 and UDP are I...