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Wireshark-users: Re: [Wireshark-users] SMB problems when ICMP is blocked?

From: "Feeny, Michael (GWMT-TASCS)" <michael_feeny@xxxxxx>
Date: Fri, 12 Mar 2010 17:15:00 -0500

First, thanx so much for your responses.  It's ALWAYS good to get ideas from fellow packeteers :-)

Now, for the Epilogue...

It turns out that the ICMP-blocking was NOT the root cause of the problem (though I had lots of evidence that pointed me in that direction).

The root of the problem was:

There was overlapping IP Address space among the many clients of this file server (this fact did not surface until much interrogation).  The client IP's were NAT'd on their way to the server in a "many-to-one" configuration.  That is, 2 different clients in the overlapping IP Address space could arrive at the server sourced with the same NAT'd IP Address.  When this occurred, as the second client arrived with the same IP as an existing client, the file server killed the first client's connection and serviced the second (and so on for the 3rd, 4th, etc.  Each one bumping off the previous connection).

The TACTICAL solution was to configure the file server to detect duplicate connections based upon machine name, and not by IP Address.

The strategic solution will be to eliminate the overlapping IP Address space, but that may take some time (we are merging 2 HUGE organizations).

Thanx again for all your feedback - I always learn a lot from the conversations here.


Michael Feeny 
Bank of America / Merrill Lynch
Global Wealth Management Technology 
Technology Architecture, Strategy & Core Services 
Application Infrastructure Services
Office: 609-274-2761 
Mobile:  484-995-1745 
AOL IM: feenyman99 

-----Original Message-----
From: wireshark-users-bounces@xxxxxxxxxxxxx [mailto:wireshark-users-bounces@xxxxxxxxxxxxx] On Behalf Of Jens Link
Sent: Sunday, March 07, 2010 4:32 PM
To: Community support list for Wireshark
Subject: Re: [Wireshark-users] SMB problems when ICMP is blocked?

Andrew Hood <ajhood@xxxxxxxxx> writes:

> You are preaching to the choir Jens. Once upon a time someone told
> security a fable about all ICMP being the tool of evil hackers. They
> believed it. IPv6 won't affect this network unless IPv4 is deleted by M$
> from all versions of the Windows stack.

Microsoft is heavily using IPv6. I usually don't work with Microsoft
products  but I was told that current Microsoft products will only talk
IPv6 to each other and if they don't have IPv6 they'll tunnel over
IPv4. It's time for a lot of people to a) IPv6 and b) TCP basics. And b)
includes not block each and *every* ICMP packets. No matter if it is
IPv4 or IPv6. 


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