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Re: IPS vs. Firewalls (why vs. ?)
From: Gabriele Buratti <gabriele.buratti () netasq com>
Date: Fri, 03 Feb 2006 14:14:01 +0100

Parental advisory: explicit vendor opinions may occour in this message !
Let me show show how IPS firewall market is seen from a IPS firewall
vendor perspective. I've been following this mailing list for 3 years
and few vendor opinions popped up. I don't know if this is because it's considered a kind of advertising (thus unpolite) or what ... (in this case list admins, please drop this mail) Let me invite my competitors in a friendly discussion about this layer 7 thing :)

Here's the thing:
1) Proxy firewalls: Proxy firewalls are in theory good because they can
do rfc compliance checks and "strange things won't be forwarded"
approach aka the marketing "day-0 protection". More, they'll do fragment
reassembly. The problems about proxies are:
- performance decreased due to complete session rewrite
- when used as reverse proxies for incoming connections you always have
that listening ports on the proxy-firewall. Listening ports means
attackable ports.

2) Firewalls with signatures: just the old IDS signatures, but now
inline. The problems with signatures are:
- keep the number of signatures low or it'll be a bottleneck thing
(false negatives)
- false positives
- any variation of a know attack signature will be a new signature

3) new technologies:
- reassemble the fragments in a separate space, do the checks, then if
ok send the fragments (no session rewriting).
- focus on the "strange things won't be forwarded", rather than
signatures: faster, sharp, you can use the marketing wizard's "0-day
protection" word :)
- decode recursively to stop blended attacks
- don't use a proxy: check on the fly and if test is passed then forward the packet (so no session rewrites and no dangerous listening ports)

        Gabriele

Marcus J. Ranum wrote:
I'd suggest you have them ask a few of the IPS vendors if they recommend
using their product in that manner. Unless you're talking to the IPS vendors
that are basically selling a firewall+signatures (like a "deep packet inspection"
firewall) they will backpedal away from that very rapidly. Perhaps your
path of least resistance is to tell them that you want one of the new
generation "IPS firewalls" then you can turn off the IPS crap (which
won't do anything except slow the firewall down, anyhow) and use the
firewall rules.

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