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    What is Firewall?

    Introduction to Firewalls

    A firewall is a device that is placed between the Internet and an internal network. Information that comes in or out must go through this firewall. The main purpose of a firewall is to keep unauthorized access (inside and outside) from unauthorized access. The configuration of the firewall depends on the policy (policy) of the organization concerned.

    A firewall is a tool to implement a security policy. Whereas security policy is made based on the balance between the facilities provided and the security implications. The tighter the security policy, the more complex the configuration of information services or the fewer facilities available on the network. Conversely, with more facilities available or in such a simple configuration that is applied, the easier it is for people to be nosy from outside to enter the system (a direct result of weak security policies).

    A firewall works by observing IP (Internet Protocol) packets that pass through it. Based on the configuration of the firewall, access can be arranged based on IP address, port, and information direction. The details of the configuration depend on each firewall. A firewall can be in the form of hardware that is already equipped with certain software, so that the user (administrator) only needs to configure the firewall. A firewall can also be software that is added to a server (both UNIX and Windows NT), which is configured as a firewall.

    Firewalls can basically be categorized into 2 based on how their functions work (both can be done on a computer device (device) or done separately), namely:

    1. Filtering function

    Firewalls work at the network level (network-level firewall) commonly called a packet filter.
    This type of firewall is usually a router that performs packet filtering functions based on certain parameters: source address, protocol, port number and contents. From comparing the information obtained in the traffic packages with the wisdom in the access table, the action taken is:
    • Pass the data packet to its destination (client or server)
    • Block data packages

    2. Proxy function

    Firewall at the application level (application level gateway) functions as a liaison between client computers with external networks. In connection, IP packets are never forwarded directly, but are translated and represented by the application gateway which functions as a channel and translator and replaces client functions.

    The proxy will relay all requests from the client to the real server, then relay all the results of the server's real response to the client again. In the middle of the above process, the proxy server has the opportunity to restrict "relays" based on the access table that has been created.

    The proxy function can be performed by various software depending on the type of proxy needed, for example web proxy, rlogin proxy, FTP proxy and so on. On the client side, certain software is often needed in order to use this proxy server, such as using SOCKS. Some UNIX-based software for proxies include: Socks (proxy server by NEC Network Systems Labs), Squid (web proxy server).


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