Firewall is a security device deployed at the boundary of an organization’ s network to protect it from unauthorised external access. It links an organization’s intranet to the internet and restricts the type of traffic that it will pass, thus providing security. Simple firewalls may be implemented in some routers, called packet filtering firewalls, they pass only some packets based on simple specified criteria such as

-Type of access (such as email, ftp, telnet as determined by

TCP port number)

-Direction of traffic

-Source or destination IP address

-Time of day


Proxy Application Gateway

Proxy application program running on a firewall machine is the one which acts on behalf of all members of an organization wanting to use the internet.

This program monitors all requests – allows access to only designated addresses outside, limits use of certain browsers and disallows use of some protocols with known security holes. Proxy application program may also be allowed to run on some user’s machine who have authorization for internet use.


Hardened Firewalls With Proxy Application Gateway

Any one from inside or outside an organization give their user id, password, service required to the firewall machine which acts as one’s proxy (ie.does ones work on his behalf). Proxy firewall is now server to the requestor’s desktop PC and also a client to some other requested service acting on requestor’s behalf. Firewall needs proxy agent for each service requested such as FTP, HTTP, TELNET etc. Now proxy firewall is the initiator of all sessions and thus knows every activity – thus ensuring security.

Firewall with a proxy function replaces the source address of transaction requestor with its own IP address -this ensures that others on internet see only firewall’s IP address – all other IP addresses of organization are hidden







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