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Circuit-level gateway

(also session layer, layer 5)

Circuit-level gateway definition

A circuit-level gateway is a network security device that operates at the transport layer of the OSI model. First, it establishes a circuit between two devices, usually with the Transmission Control Protocol (TCP). Then, it monitors the communication to determine whether to allow or block the connection based on the source, destination IP addresses, and the source and destination ports. Finally, the circuit-level gateway terminates the connection if the traffic flow doesn’t conform to the original parameters. Circuit-level gateways differ from other types of firewalls because they operate at higher abstraction levels and base their decisions on connection-level information. Consequently, they provide better performance and an additional security layer.

Circuit-level gateway advantages

  • Improved performance. Circuit-level gateways operate at a lower layer of the network protocol stack and base their decisions on connection-level information, thus delivering better performance.
  • Easier to configure. Circuit-level gateways don’t require complex rules for individual applications or services, so they are typically easier to configure.
  • Lower risks. Circuit-level gateways limit the exposure of internal systems and applications to external network traffic, thus providing an additional layer of security.

Circuit-level gateway disadvantages

  • Limited functionality. Circuit-level gateways provide basic filtering capabilities and are less sophisticated than other types of firewalls.
  • Vulnerable to protocol attacks. They are vulnerable to attacks that exploit weaknesses in network protocols which can bypass the circuit-level filtering mechanisms, such as TCP/IP.
  • Limited visibility. Circuit-level gateways don’t provide detailed information about individual packets or network traffic, making it difficult to troubleshoot network issues.