..::You can change the world with the knowledge::..

Proxy server is a computer server or computer programs that can act as the other computers to make requests to the content of the internet and intranet (http://id.wikipedia.org/).
Proxy server acts as a gateway to the world of the Internet for each client computer. In carrying out its proxy server is invisible to the client computer as an example when a user interacts with the Internet via a proxy server will not know that a proxy server is handling requests are done. Web server that receives requests from the Proxy server will menginterpresentasikan these requests as if it came directly from the client computer, instead of the proxy server.

Proxy server in a network has three main functions namely as a Connection sharing, filtering, and caching.
a. Connection Sharing 
In a local network connected to other networks or the Internet, users do not directly relate to external networks or the Internet, but must pass through a gateway, which acts as a boundary between a local network (private) and external networks (the public). Gateway is very important, because the local network must be well protected from the dangers that may come from the internet, and it will be difficult if there are no clear boundaries between local networks and the Internet. Gateway also acts as the point where the number of connections from local users will be connected to him, and a connection to the outside network is also connected to him. Thus, the connection of local networks to the Internet will use a connection that is owned by the gateway together (connection sharing). In this case, the gateway is also a proxy server, as it provides services as an intermediary between the local network and external networks or the Internet. in short: a public IP can be used by multiple users, (IPv4 is running out used .... let's migration to IPv6 ... ..) but also to protect the network from outside attacks.
b. Filtering 
is a business or security restrictions so that the existence of a filtering proxy servers can secure and restrict client access rights on a private network. So even though initially created as a non sekurity cache, the main purpose of the proxy server is now a firewalling. Proxy server update service requests on the external network on behalf of their clients on a private network. This automatically hides the identity and number of clients on the internal network from external networks. Because of their position in the client's internal and public server, the proxy also can store frequently accessed content from the public network to reduce public access to the network. Most real implementations include security proxy packet filtering and Network Address Translation to build a firewall intact. Such technology can be combined with a proxy to eliminate attacks against vulnerable proxy.
c. Caching (Internet Object caching) 
is a way to save the internet query-object. (Such as: data from the HTTP, FTP, and ghoper protocol) to make the system closer to demand than to the original source. Web browsers can use the local Squid cache as a proxy HTTP server, this will reduce the access time as well as bandwidth savings. In other words, a client should not make contact with the server to request services but the client can get the service (data) that has been stored on the proxy server, with this then access will be faster.

Squid 
Squid is a free UNIX-based public domain. function of the squid is to'cache 'or storing data requested by the user (client computer) is usually in the form of web pages and FTP. Supported UNIX platforms by Squid is FreeBSD, BSDI, Digital Unix, Irix, Linux, Solaris and SunOs. Not all data can be cached by the Squid, the data is dynamic such as CGI-BIN is not cached by Squid, so each time a request CGI-BIN, then Squid will directly contact the destination server. Currently the protocol that can be serviced by the Squid is HTTP, FTP, Gopher and Wais.

NAT (network address translation) 
Network Address Translation or commonly referred to as NAT is a method to connect more than one computer to the Internet network using a single IP address. Much use of this method due to the limited availability of IP addresses, security needs (security), and the ease and flexibility in network administration. With NAT, a large network can be broken down into smaller networks. Small parts that each have a single IP address, so we can add or reduce the number of computers without affecting the overall network. In addition, the modern gateways NAT DHCP server exists that can automatically configure the client computer. This is very advantageous for the network admin to change the configuration for the network, admins just need to change on a computer server and these changes will happen on all client computers. NAT gateway is also able to restrict access to the internet, while also able to record all traffic to and from the internet. Overall, with all the advantages of NAT gateway, the network admins will be very helpful in performing his duties.