Circuit-level gateway

A circuit-level gateway is a type of firewall.

Circuit-level gateways work at the transport layer of the OSI model, or as a "shim-layer" between the application layer and the transport layer of the TCP/IP stack. They monitor TCP handshaking between packets to determine whether a requested session is legitimate. Information passed to a remote computer through a circuit-level gateway appears to have originated from the gateway. Circuit-level firewall applications represent the technology of next to first generation. Firewall technology supervises TCP handshaking among packets to confirm a session is genuine. Firewall traffic is clean based on particular session rules and may be controlled to acknowledged computers only. Circuit-level firewalls conceal the network itself from the external, which is helpful for interdicting access to impostors. But circuit-level firewalls do not clean entity packets. This is useful for hiding information about protected networks. Circuit-level gateways are relatively inexpensive and have the advantage of hiding information about the private network they protect. On the other hand, they do not filter individual packets.

See also

• Application firewall
• Application-level gateway firewall
• Bastion host
• Dual-homed

External links

• http://netsecurity.about.com/cs/generalsecurity/g/def_circgw.htm
• http://www.codepedia.com/1/Circuit-level+gateway
• http://www.softheap.com/internet/circuit-level-gateway.html
• http://www.pcstats.com/articleview.cfm?articleid=1450&page=5