, . , , (screening router), (packet filter).
(router) - , . , , . .
, , , . , - , ( hop - ), , . , , ICMP .
, , , . , , , ( ), , , .
, , - Internet Telnet . , - , , - . . Telnet- . , . 2.1, Telnet.
(stateless packet filtering), ‑ . , (stateful packet filtering stateful inspection), .
, , , . , ! .
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, . , , , . , .
. 2.1. , Internet
, , , ! . , log-.
proxy-
. , , . , , . , , - , , FTP. , - get () put (). , , .
(application gateway), proxy- (application proxy), , , . , proxy- , .
proxy- . , , proxy-. , , proxy-. , . , Netscape Navigator Microsoft Internet Explorer proxy-.
, proxy-. , Telnet proxy-, . , , , proxy-.
proxy-, Trusted Information Systems Firewall Toolkit (FWTK) SOCKS. SOCKS - , proxy- SOCKS. TIS Firewall Toolkit proxy- , Telnet, FTP HTTP.