Re: mail service with no mx (was - Re: Computer systems blamed forfeeble hurricane response?)
Date: Tue Sep 13 19:34:32 2005
On Wed, 14 Sep 2005, Roy Badami wrote:
william(at)elan> Could you elaborate on how firewall will
william(at)elan> determine if the connection is from mail server
william(at)elan> or from telnet on port 25?
Perhaps because most telnet clients will attempt telnet option
negotiation? If so one could avoid this by using a client such as
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.