Proxy Server Functionality

Act as an intermediary between hosts Cache data to reduce the time and external bandwidth required to service requests
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Proxy Server FunctionalityProxy Server FunctionalityIn the context of firewalls, proxy servers (proxies) have a couple of primary functions: • Act as an intermediary between hosts • Cache data to reduce the time and external bandwidth required to service requestsProxies act as an intermediary by literally intercepting and responding to requestsbetween hosts, as shown in Figure 8-1. Figure 8-1. Communication Process Between Hosts Through a Proxy [View full size image]In this case, Server1 and Server2 are attempting to communicate with each other. Theproxy resides between the two hosts and responds to all communications and requestsbetween the two hosts. This ensures that the two hosts never actually communicatedirectly with each other. Logically, Server1 and Server2 are communicating with eachother, even though physically the communication process is occurring through a proxy.This function is completely transparent to the end user/system, which means that Server1has no idea that it is not actually communicating directly with Server2 and vice versa.Many proxies, in particular proxies that support the HTTP protocol, can also cache data,which in turn allows the proxy to service subsequent requests for the same data fromcache, instead of needing to forward the request to the external source. This allows theproxy to help reduce Internet bandwidth requirements, because the first request for thedata uses Internet bandwidth whereas all subsequent requests are services from theproxys cache. This has the additional effect of reducing the time that it takes to displaythe data because many proxies are connected to the clients that use them over fasterconnections.These two elements, application filtering and functioning as a proxy, are the twoelements that really identify an application proxy firewall from other types of firewallssuch as deep packet inspecting firewalls.