[84493] in North American Network Operators' Group
Re: mail service with no mx (was - Re: Computer systems blamed for feeble hurricane response?)
daemon@ATHENA.MIT.EDU (Steven M. Bellovin)
Tue Sep 13 21:35:29 2005
From: "Steven M. Bellovin" <smb@cs.columbia.edu>
To: Adam McKenna <adam@flounder.net>
Cc: nanog@nanog.org
In-Reply-To: Your message of "Tue, 13 Sep 2005 16:59:50 PDT."
<20050913235950.GA16550@flounder.net>
Date: Tue, 13 Sep 2005 21:32:25 -0400
Errors-To: owner-nanog@merit.edu
In message <20050913235950.GA16550@flounder.net>, Adam McKenna writes:
>
>On Tue, Sep 13, 2005 at 04:31:05PM -0700, william(at)elan.net wrote:
>> Telnet option negotiation is at Layer 7 after TCP connection has been
>> established. Firewalls typically don't operate at this level (TCP session
>> is Layer 4 if I remember right) and would refuse or reject (difference
>> type of ICMP response) based solely on attempt to connect to certain
>> ip or certain TCP/UDP port.
>
>Application layer firewalls have existed for at least 6 years.
>
Make that 15....
--Steven M. Bellovin, http://www.cs.columbia.edu/~smb
