RE: TCP: Syn Flooding Issue
- From: "Amy Babinchak" <amy@xxxxxxxxxxxxxxxxxxxxxxxxxx>
- To: "[ISAserver.org Discussion List]" <isalist@xxxxxxxxxxxxx>
- Date: Thu, 23 Dec 2004 19:11:05 -0500
I just inherited this client on Tuesday. Nothing like being under fire!
Today I ran network monitor for tcp and discovered that the reception
computer was firing out 10 times more packets than the rest and no one
was even logged into it. I powered it off and about 3/4 of the tcp syn
flood reports from the firewall stopped immediately and the network sped
up dramatically. That machine is now sitting in a locked room all by
itself, hopefully thinking about the bad things it's done. I'm still not
to the bottom of the issue but at least they can work now - well except
for the receptionist. Nothing unusual appeared to be running in task
manager so I'm not sure if I'm looking at a bad nic or a worm. I leaning
toward worm even though I can't see it.
I haven't look much further than resolving issues of synchronization and
this flooding problem. But I believe that there may be DFS or at least
off-line sync trying to happen. There are some errors in the logs on
this topic on the server but I haven't looked at them closely yet.
Something I need to know about DFS and 445? I thought that DFS was a bad
idea over a wan because it doesn't have a way to alert you of possible
data change conflicts if the file was changed by two different people.
Amy
-----Original Message-----
From: josephk [mailto:josephk@xxxxxxxxx]
Sent: Thursday, December 23, 2004 4:06 PM
To: [ISAserver.org Discussion List]
Subject: [isalist] RE: TCP: Syn Flooding Issue
http://www.ISAserver.org
Hi Amy,
I still close down 445 for every machine except the AD boxes.
And the machines actually don't get hit with the sync errors.
Are your sites using DFS or anything like that?
Thank you,
Joseph
-----Original Message-----
From: Amy Babinchak [mailto:amy@xxxxxxxxxxxxxxxxxxxxxxxxxx]
Sent: Thursday, December 23, 2004 5:38 AM
To: [ISAserver.org Discussion List]
Subject: [isalist] RE: TCP: Syn Flooding Issue
http://www.ISAserver.org
There is 1 server at each office. There are 4 office total. The offices
are connected over VPN.
Here's that section of the log.
Thur, 12/23/2004 05:40:16 - 445 dropped - Source:10.1.2.10, 6166, LAN -
Destination:10.1.4.10, 445, WAN
Thur, 12/23/2004 05:40:22 - 445 dropped - Source:10.1.2.10, 6169, LAN -
Destination:10.1.3.10, 445, WAN
Thur, 12/23/2004 05:40:22 - 445 dropped - Source:10.1.2.10, 6172, LAN -
Destination:10.1.1.10, 445, WAN
They only try once every 6 to 20 minutes so this isn't the clog. I was
just wondering by blocking this what communications between the servers
am I preventing? I know that 445 is SMB but I don't know what domain
functions are dependant on SMB besides network places browsing. Are
there any?
Amy
Harbor Computer Services
Small Business Computer Specialists
Office (248) 546-6056
Mobile (248) 890-1794
-----Original Message-----
From: Thomas W Shinder [mailto:tshinder@xxxxxxxxxxx]
Sent: Thursday, December 23, 2004 8:26 AM
To: [ISAserver.org Discussion List]
Subject: [isalist] RE: TCP: Syn Flooding Issue
http://www.ISAserver.org
Hi Amy,
Which servers are trying to sync?
Where are the source and destination servers?
Thanks!
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: Thursday, December 23, 2004 7:15 AM
To: [ISAserver.org Discussion List]
Subject: [isalist] RE: TCP: Syn Flooding Issue
http://www.ISAserver.org
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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