What is Application Level Firewall (Application Gateway) ?

 Application level firewall (Application Gateway) is a part of a proxy server. Application gateways do not allow any packets to pass directly between the two networks they connect. Instead, proxy appliactions running on the firewall computer forward requests to services on the private network. Then forward responses to the originators on the unsecured public network. Application gateways authenticate the credentials of a user before allowing access to the network. They are auditing and logging mechanisms as part of the security policy. Application gateways require some configuration on the part of users to able their client machines to function properly. For example, if a File Transfer Protocol (FTP) proxy is configured on an application gateway, it can be configured to allow some FTP commands but deny others. One could configure a SMTP (Simple Mail Transfer Protocol ) proxy on an application gateway that would accept mail from the outside (without revealing internal e-mail addresses), and then forward the mail to the internal mail server. However, because of the additional processing overhead, application gateways have advanced hardware requirements and are slower than network-level firewalls.