Firewall Technology 2 (PROXY SERVER)

PROXY SERVER

As the name states proxy server, here the server is being reached by using Proxy. The connection established by proxy on behalf of Client.

CLIENT-------------------------------------------PROXY-----------------------------------------SERVER

Here, Client when has to access any traffic of Internet, it sends request to proxy initially, proxy manages the traffic and sends it to dedicated server on behalf of client. Proxy acts as server for client and Client for the destination Server. All the tcp traffics are managed by Proxy. 

A proxy server is a server that sits between a client application, such as a Web browser, and a real server. It intercepts all requests to the real server to see if it can fulfill the requests itself. If not, it forwards the request to the real server.

Proxy Servers add security to the content. It helps in application level filtering of the data send from client to Server. Proxy Servers are slow henceforth, as it adds extra filtering to the content, also helping in securing the content.

Proxy Servers are of 3 Types

• Application Level Proxy- Application level proxy is also known as Application Gateway. Whereas, an application gateway is an application program that runs on a firewall system between two networks. When a client program establishes a connection to a destination service, it connects to an application gateway, or proxy. The client then negotiates with the proxy server in order to communicate with the destination service. In effect, the proxy establishes the connection with the destination behind the firewall and acts on behalf of the client, hiding and protecting individual computers on the network behind the firewall. This creates two connections: one between the client and the proxy server and one between the proxy server and the destination. Once connected, the proxy makes all packet-forwarding decisions. Since all communication is conducted through the proxy server, computers behind the firewall are protected. While this is considered as most secure method, but application gateway require more memory and processor requirements.
• Web Proxy-A common proxy application is a caching Web proxy. This provides a nearby cache of Web pages and files available on remote Web servers, allowing local network clients to access them more quickly or reliably.When it receives a request for a Web resource (specified by a URL), a caching proxy looks for the resulting URL in its local cache. If found, it returns the document immediately. Otherwise it fetches it from the remote server, returns it to the requester and saves a copy in the cache.Cache usually uses expiry algorithm to remove documents from cache, according to their size, age and access history. Algorithms like LRU (Least Recent Used) and LFU (Least Frequently used) are implemented.Web proxies can also filter the content of Web pages served. Some censorware applications - which attempt to block offensive Web content - are implemented as Web proxies.
• Email Proxy-Email proxy uses SMTP (Simple Mail Transfer Proxy) Agents to transfer mails to other agents. SMTP proxies do not store messages like a mail transfer agent (MTA) does, they can reject SMTP connections or message content in real-time. Certain SMTP proxies implement TCP connection management (otherwise known as flow control), which can help to reduce damage to downstream mail servers resulting from spikes in TCP traffic from malicious SMTP clients. TCP connection management in the context of SMTP typically involves bandwidth throttling and/or introducing delays in SMTP command responses. When slowed down, certain malicious sources of SMTP traffic such as spam bots tend to give up rather than continuing to deliver a full email message.