RE: TCP: Syn Flooding Issue
- From: "Amy Babinchak" <amy@xxxxxxxxxxxxxxxxxxxxxxxxxx>
- To: "[ISAserver.org Discussion List]" <isalist@xxxxxxxxxxxxx>
- Date: Thu, 23 Dec 2004 08:15:03 -0500
I added the 445 port and then blocked it just so I could determine if
there was any 445 traffic coming from inside. (Without the service added
the firewall doesn't log anything from an internal address.) Overnight I
see that the servers are trying to communicate using 445 once every 15
minutes and only once to each server. This looks like an active
directory sync. If I continue to block 445 will the servers still be
able to sync with each other?
Amy
-----Original Message-----
From: Thomas W Shinder [mailto:tshinder@xxxxxxxxxxx]
Sent: Wednesday, December 22, 2004 10:19 PM
To: [ISAserver.org Discussion List]
Subject: [isalist] RE: TCP: Syn Flooding Issue
http://www.ISAserver.org
Hi Joseph,
I'm guessing the problem isn't that the connections are overtaxing the
firewall, but that the customer's end of the pipe is full with what is
essentially a DDoS. The *only* was to solve the DDoS issue is by having
the ISP block the connections from the fat end of the pipe, 'cause
there's nothing you can do on your end. The ISP can block via IP address
(which gettings pretty hard with DDoS's) but much easier if they're all
going for the same port.
Tom
www.isaserver.org/shinder
Tom and Deb Shinder's Configuring ISA Server 2004
http://tinyurl.com/3xqb7
MVP -- ISA Firewalls
-----Original Message-----
From: josephk [mailto:josephk@xxxxxxxxx]
Sent: Wednesday, December 22, 2004 7:22 PM
To: [ISAserver.org Discussion List]
Subject: [isalist] RE: TCP: Syn Flooding Issue
http://www.ISAserver.org
Hi Amy,
What kind of firewall? Watchguard or something like that?
If, it's watchguard you can bock the incoming 445 from
The VPN connections and that should eliminate most
Of the strange hits.
Joseph
-----Original Message-----
From: Amy Babinchak [mailto:amy@xxxxxxxxxxxxxxxxxxxxxxxxxx]
Sent: Wednesday, December 22, 2004 4:36 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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