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All Forums >> [ISA 2006 General] >> Installation and Planning >> RE: WHY NOT TO BUY ISA SERVER. Page: <<   < prev  1 [2]
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RE: WHY NOT TO BUY ISA SERVER. - 24.Oct.2008 7:26:34 AM   


Posts: 380
Joined: 19.Oct.2008
Status: offline
Speaking about DoS, there is a nice aspect regarding ISA's application filters and TCP connections. For example, when you publish a server behind ISA, and an application filter exists for that protocol(assuming the correct server publishing rule was used), even if this server "has" a "sensible" backlog, and a crafted SYN flood is used "to fill" this backlog, the server will be protected.
When the application filter is bound to the server publishing rule, ISA "proxies" the TCP SYNs(either for a NAT or route network relationship), if we only focus on this aspect. Thus no SYNs will reach the back server if the "clients" are not able to complete the TCP three-way handshake. Too bad there aren't more application filters...
Others have implemented a form of TCP SYN-proxy(Cisco, Juniper or OpenBSD to name  few).
The fun stuff is that with ISA, the "SYN-proxy" is on by default if the correct server publishing rule is used. Their advantage is that they can apply "SYN-proxy" for TCP connections to any destination ports.
"Enabling" application layer filtering on other devices, may not translate into "SYN-proxy operations", an extra touch being required on those devices, to compensate the hybrid model.
Interesting, scrolling through those docs(various platforms), we can notice a lot of "firewall things" that ISA does by default, without requiring any user "input".


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(in reply to Jim Harrison)
Post #: 21
RE: WHY NOT TO BUY ISA SERVER. - 28.Oct.2008 7:25:48 AM   


Posts: 50013
Joined: 10.Jan.2001
From: Texas
Status: offline
Hi Adrien,

Great info!



Thomas W Shinder, M.D.

(in reply to adimcev)
Post #: 22

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