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

  • From: Adam McKenna
  • Date: Tue Sep 13 20:01:31 2005

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.

--Adam




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