13 Sep
2005
13 Sep
'05
9:32 p.m.
In message <20050913235950.GA16550@flounder.net>, Adam McKenna writes:
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.
Make that 15.... --Steven M. Bellovin, http://www.cs.columbia.edu/~smb