Merit Network
Can't find what you're looking for? Search the Mail Archives.
  About Merit   Services   Network   Resources & Support   Network Research   News   Events   Home

Discussion Communities: Merit Network Email List Archives

North American Network Operators Group

Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical

Re: mail service with no mx (was - Re: Computer systems blamed forfeeble hurricane response?)

  • From: Crist Clark
  • Date: Tue Sep 13 20:44:26 2005

Adam McKenna wrote:
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.
AAAAAAAAAAAGGGGGGGGGGHHHHHH!

But the point is that you would still establish a TCP connection
before a MTA, firewall, IPS, or whatever could know it was telnet!
The FEMA address that started this whole thing was timing out. You
can tell the difference between a telnet filter and something
completely, silently blocking 25/tcp.

CAN THIS DIE NOW? Pulllleeeeeese...
--
Crist J. Clark                               crist.clark@globalstar.com
Globalstar Communications                                (408) 933-4387




Discussion Communities


About Merit | Services | Network | Resources & Support | Network Research
News | Events | Contact | Site Map | Merit Network Home


Merit Network, Inc.