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Re: Computer systems blamed for feeble hurricane response?

  • From: Steven M. Bellovin
  • Date: Tue Sep 13 16:39:41 2005

In message <20050913202040.GK16110@core.center.osis.gov>, Joseph S D Yao writes
:
>
>On Tue, Sep 13, 2005 at 04:15:29PM -0400, Mike Tancsa wrote:
>> At 03:50 PM 13/09/2005, Joseph S D Yao wrote:
>> 
>> >Oh, and also ... please consider that some firewalls try to discern
>> >whether the connection on port 25 is from a mail server or from Telnet.
>> >While I mourn the simplicity of manual debugging of such sites, it
>> >remains that: the fact that you can't TELNET HOST.DOMAIN 25 doesn't mean
>> >that there's no mail service there.
>> 
>> Making a network connection using the application "telnet" vs the 
>> application "sendmail" (or whatever MTA one uses) seems to be the 
>> same when doing a tcpdump on the data.  I am not sure how a firewall 
>> would know -- purely at the network layer -- what the other side's 
>> application was/is that initiated the connection.  Yes, the other end 
>> could try and connect back to the host, but there is no 2 way traffic 
>> as the 3way handshake is not completing and I dont see any other 
>> traffic coming back from that host attempting to discern any info.
>
>
>I don't know, myself.  I said they try.  Perhaps they succeed.  Perhaps
>they check the speed of incoming queries.  Perhaps they try to use a
>Telnet OPTION.  I don't know.  Perhaps it's a sales gag.  [I think it
>was a telnet OPTION, actually.]
>

Telnet options, and for that matter speed, happen after the 3-way 
handshake.  We're not getting that far.

		--Steven M. Bellovin, http://www.cs.columbia.edu/~smb






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