On Tue, Sep 13, 2005 at 04:31:05PM -0700, william(at)elan.net wrote:
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.
You're talking about the packet filters that marketeers sell as "firewalls". The best firewalls operate at the application layer. And, yes, that's an OPINION, no need to rave. -- Joe Yao ----------------------------------------------------------------------- This message is not an official statement of OSIS Center policies.