Perhaps the biggest advantage of using an ALG is the degree of protection it provides for corporate networks. Here are some of the advantages offered by ALGs: 1. Once the user is authenticated, the gateway will access the remote host on their behalf to deliver the data packets required for the application.ĭue to their enhanced security, ALGs are becoming increasingly popular with organizations of all types-especially as the cybersecurity landscape becomes more threatening. The gateway will then authenticate-or deny-the user based on their login credentials. The ALG verifies the user’s authenticity.The gateway will also request login credentials, such as a username and password. Once the user makes contact with the gateway, it will ask about the remote host they are trying to establish a connection with. First, a user must contact an application gateway using a TCP or IP application. Here’s a step-by-step guide to how ALGs work: They also allow applications to use dynamic ports like TCP and UDP to communicate with known ports used by server applications. They manage specific application protocols such as session initiation protocol (SIP) and file transfer protocol (FTP). How Application-Level Gateways WorkĪpplication gateways perform various functions on layer 7 of a network infrastructure. These tools filter messages at the application layer 7 of the OSI model. ALG solves this problem at the application layer by replacing the internal IP with the address of the NAT interface.Application-level gateways (ALGs), also known as application proxies or simply application gateways, are software components that augment a firewall or network address translation (NAT) within a computer network. FTP port commands use IP addresses that are configured on endpoint interfaces, which in the case of a host behind a NAT firewall is usually unreachable from the Internet. In this case, the endpoints do not always realize that their addresses are being translated midstream.
Once the session is complete, the gateway closes immediately.įTP ALG also handles the special case when an FTP session passes through a NAT interface.
ALG dynamically opens a specific combination of source and destination IP ports in the firewall policy that allows a session to be established. Because these data channels can connect to any port, it is almost impossible to create a static firewall policy that allows these data channels and still provide adequate protection.įTP ALG automatically solves this problem by monitoring the FTP command channel, looking for FTP port commands that indicate which source and destination ports are being requested.
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