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

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 netcat...

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. -- William Leibzon Elan Networks william@elan.net