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From: Valdis.Kletnieks at vt.edu (Valdis.Kletnieks@...edu)
Subject: closing ports 

On Fri, 07 Nov 2003 15:30:56 +0200, hena <hena@...k.fi>  said:
> if your running linux try something like
> iptables -t filter -A INPUT -p tcp -s 0.0.0.0 --syn -j REJECT
> --reject-with tcp-reset

that -s 0.0.0.0 won't do what you think. (It will drop all packets
that have a source address of 0.0.0.0).  I'd not bet on getting
right results from '-s 0.0.0.0/0' either. You probably want to:

a) Leave the -s 0.0.0.0 off entirely.
b) Make this the *last* rule, and have other accepting rules before it.
c) Include a ' -m limit --limit 4/sec -j LOG' rule or similar, so you know
what it is you're dropping on the floor.
d) Actually *LOOK AT* what (c) produces (yes, a daily summary via Perl script
is OK).

Many sites don't bother doing (d) and then get surprised when they get
blindsided by something that the logs had given fair warning for....
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