I don't consider it a "business class" firewall at all. However, the final question about blocking intrusion: yes, you can set up pretty comprehensive access-lists to restrict and control access to a point. However, the other things which makes a box a firewall will always be missing.
As far as DoS attacks, I think it would crack with almost no effort at all. Such a small box will be pretty busy with legitimate traffic, let alone trying to fend of a DoS attack.
Unless you can upgrade this device with the Cisco IOS Firewall feature set (and I don't think it can), I wouldn't use it as a firewall for anything above SOHO or small office use. Even then, I'd be darned sure the customer understands the position he will be in.
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...