[84456] in North American Network Operators' Group
Re: Computer systems blamed for feeble hurricane response?
daemon@ATHENA.MIT.EDU (Mike Tancsa)
Tue Sep 13 16:19:31 2005
Date: Tue, 13 Sep 2005 16:15:29 -0400
To: Joseph S D Yao <jsdy@center.osis.gov>
From: Mike Tancsa <mike@sentex.net>
Cc: nanog@nanog.org
In-Reply-To: <20050913195012.GE16110@core.center.osis.gov>
Errors-To: owner-nanog@merit.edu
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.
---Mike
