RE: TCP: Syn Flooding Issue
- From: "Amy Babinchak" <amy@xxxxxxxxxxxxxxxxxxxxxxxxxx>
- To: "[ISAserver.org Discussion List]" <isalist@xxxxxxxxxxxxx>
- Date: Wed, 22 Dec 2004 20:13:18 -0500
I'm not sure; could be worm. Does it matter?
They go for 135 and 139 too but there's not nearly as many of those in
the log as 445.
Amy
-----Original Message-----
From: Thomas W Shinder [mailto:tshinder@xxxxxxxxxxx]
Sent: Wednesday, December 22, 2004 8:07 PM
To: [ISAserver.org Discussion List]
Subject: [isalist] RE: TCP: Syn Flooding Issue
http://www.ISAserver.org
Hi Amy,
Are you sure these are actually SYN flood attacks or just the Direct
Host 'worm du jour'. If they are actually flooding your pipe with these
connection requests, then there's really nothing you can do on your end.
Since there's no legit use for inbound TCP 445 over the Internet, you
can ask your ISP to shut down connections to that port for your public
address. We done this a few times for folks who were DDoS'ed and its
really the only solution. At least they're just going for a non-Internet
protocol; it would be rotten if they were using 135 or 25.
HTH,
Tom
www.isaserver.org/shinder
Tom and Deb Shinder's Configuring ISA Server 2004
http://tinyurl.com/3xqb7
MVP -- ISA Firewalls
-----Original Message-----
From: Amy Babinchak [mailto:amy@xxxxxxxxxxxxxxxxxxxxxxxxxx]
Sent: Wednesday, December 22, 2004 6:36 PM
To: [ISAserver.org Discussion List]
Subject: [isalist] TCP: Syn Flooding Issue
http://www.ISAserver.org
I've got an office with tcp syn flooding. It slows the internet down to
a crawl and makes accessing secure websites almost impossible. It has
this real estate office almost shut down.
The weird thing is that the tide goes out of this DOS attack everyday
around 4:00. It just stops and then it starts up in the morning.
The logs show that the flood is coming from about a dozen IP addresses
on the Internet. But is it really? It seems to coincide with the end of
work day for about 1/2 of the staff.
What's the best way to get rid of a tcp syn flood attack? Should I
assume that it's external and not triggered by an internal machine?
Wed, 12/22/2004 16:17:44 - TCP connection dropped - Source:66.178.17.36,
53263, WAN - Destination:66.178.207.200, 445, WAN - 'TCP:Syn Flooding'
Wed, 12/22/2004 16:17:44 - TCP connection dropped - Source:66.178.17.36,
53263, WAN - Destination:66.178.207.200, 445, WAN - 'TCP:Syn Flooding'
Wed, 12/22/2004 16:17:46 - TCP connection dropped - Source:66.178.17.36,
53263, WAN - Destination:66.178.207.200, 445, WAN - 'TCP:Syn Flooding'
Wed, 12/22/2004 16:18:26 - TCP connection dropped -
Source:220.141.51.234, 3040, WAN - Destination:66.178.207.200, 445, WAN
- 'TCP:Syn Flooding'
Wed, 12/22/2004 16:18:28 - TCP connection dropped -
Source:220.141.51.234, 3040, WAN - Destination:66.178.207.200, 445, WAN
- 'TCP:Syn Flooding'
FYI: The firewall isn't an ISA Server (working on them to change) and
there are 3 VPN connections to other offices on this firewall.
If I can get to the bottom of this I'll be the hero and then I can put
in some ISA servers. They really need them. They've got site-to-site
VPN's, RAS, and Exchange. The place is screaming ISA.
Thanks,
Amy
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