application level gateway is also known as

Once the two connections are established, the gateway typically relays TCP segments from one connection to the other without examining the contents. As with an application gateway, a circuit-level gateway does not permit an end-to-end TCP connection rather, the gateway sets up two TCP connections, one between itself and a TCP user on an inner host and one between itself and a TCP user on an outside host. This can be a stand-alone system or it can be a specialized function performed by an application-level gateway for certain applications.

Circuit-Level GatewayĪ fourth type of firewall is the circuit-level gateway or circuit-level proxy (see Figure 9.1e). In effect, there are two spliced connections between the end users, with the gateway at the splice point, and the gateway must examine and forward all traffic in both directions. In addition, it is easy to log and audit all incoming traffic at the application level.Ī prime disadvantage of this type of gateway is the additional processing overhead on each connection. Rather than trying to deal with the numerous possible combinations that are to be allowed and forbidden at the TCP and IP level, the application-level gateway need only scrutinize a few allowable applications. Further, the gateway can be configured to support only specific features of an application that the network administrator considers acceptable while denying all other features.Īpplication-level gateways tend to be more secure than packet filters. If the gateway does not implement the proxy code for a specific application, the service is not supported and cannot be forwarded across the firewall.

When the user responds and provides a valid user ID and authentication information, the gateway contacts the application on the remote host and relays TCP segments containing the application data between the two endpoints.

The user contacts the gateway using a TCP/IP application, such as Telnet or FTP, and the gateway asks the user for the name of the remote host to be accessed. An application-level gateway, also called an application proxy, acts as a relay of applicationlevel traffic (see Figure 9.1d).

Application level gateway is also known as