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North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical Re: Computer systems blamed for feeble hurricane response?
In message <[email protected]>, 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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