gateway
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... network for the purpose of protecting it. A
firewall acts as a gateway through which all traffic to and from the
protected network ...
... traffic with particular
characteristics to pass through carefully monitored doors
("gateways"). The difficult part is establishing the criteria by
which the packets are allowed or denied access through the doors.
Books written on firewalls ...
... proxy servers,
sometimes called Application Layer Gateways (ALGs), can be written
which understand specific protocols ...
... B. Cheswick, "The Design of a Secure Internet Gateway", Proceedings of the Summer Usenix Conference, Anaheim, CA, June 1990. ...
... Mogul, J., "Simple and Flexible Datagram Access Controls for UNIX-based Gateways", Digital Western Research Laboratory Research Report 89/4, March 1989. ...