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

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