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Re: [FW-1] SMTP and Unknown Established TCP packet
I did experience that problem some time back, at a customer of ours.
We found out that SMTP connections to many sites took *long* times to
establish. We demonstrated that in that particular case the problem was
lousy service from the ISP, since many sites had problems when connections
were attempted. Connections were being dropped (out of state) since it took
longer than the "handshake" timeout to start exchanging traffic. We
worked-around it taking the 60s default timer to 300s, and advised the
customer to talk to their service provider.
If you want to make sure, download VisualRoute, install it on a laptop and
place it just outside the FW with a public IP. Then point VR to some of the
problematic sites and you may eventually see routing loops or long delays on
specific links on the way to them. They have a handy 30d eval version at
http://www.visualware.com/download/index.html.
At that time, Lance Spitzner's paper on how FW-1's connection table works
(http://www.enteract.com/~lspitz/fwtable.html) proved extremely useful. We
monitored the FW's connection table (with a Perl script that converts the
hex to decimal) while simultaneously sniffing traffic to find the cause of
the problem. But of course, that was not a Windows box... ;-)
Who knows, maybe you are experiencing that same problem. Let us know how it
went!
J.
From: [email protected]
Reply-To: Mailing list for discussion of Firewall-1
<[email protected]>
To: [email protected]
Subject: [FW-1] SMTP and Unknown Established TCP packet
Date: Wed, 27 Mar 2002 11:29:51 +0600
Hi,
I have very simple checkpoint installation with a mail gateway on DMZ.
most of my SMTP mail keeps dropping with the "Unknown Established TCP
packet" - both inbound and outbound. to rectify this I have done the
following on the fw (ver 4.1 SP6 running on NT 4.0)
In objects.c I have increased the tcpstarttimeout to 120 sec from default
60 sec
On init.def file I have added ADD_TCP_TIMEOUT (25,3600)
(Both tips I got from phoneboy)
But my problem is not solved. The smtp drops have slightly decreased but
not significantly.
When I put the smtp traffic on fast mode my problem is solved. no dropped
smtp packets! . But I dont feel this is the correct way to go about it.
So
1. What else can I do rectify this problem other than activation fast
mode? I am willing try any wild idea.
2. If my only solution is to activate fast mode , then how risky is it (or
in other words is it not recommended) ?
Thanks in advance
Nishan
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