basic networking

hi

i want to ask few question..
what is proxy server?

also, in LAN
IS there should be inculde hubs...switchs..or something else?

A proxy server is a computer that offers a computer network service to allow clients to make indirect network connections to other network services. A client connects to the proxy server, then requests a connection, file, or other resource available on a different server. The proxy provides the resource either by connecting to the specified server or by serving it from a cache. In some cases, the proxy may alter the client's request or the server's response for various purposes.

A proxy server can also serve as a firewall.

Proxy servers can dramatically improve performance for groups of users. This is because it saves the results of all requests for a certain amount of time. Consider the case where both user X and user Y access the World Wide Web through a proxy server. First user X requests a certain Web page, which we'll call Page 1. Sometime later, user Y requests the same page. Instead of forwarding the request to the Web server where Page 1 resides, which can be a time-consuming operation, the proxy server simply returns the Page 1 that it already fetched for user X. Since the proxy server is often on the same network as the user, this is a much faster operation. Real proxy servers support hundreds or thousands of users. The major online services such as Compuserve and America Online, for example, employ an array of proxy servers.

Proxy servers can also be used to filter requests. For example, a company might use a proxy server to prevent its employees from accessing a specific set of Web sites.

about LANs, it depends on what kind of a network it is. it might contain a plethora of networking nodes ranging from routers, hubs, switches, etc. it mainly depends on the topology used, and the actual size of the LAN

Arani,

Nice answer

I didn't be a user for proxy server before... i just want know when the second user use the same page what if there is some text boxe (form pages), did second user see what is first user fill in these forms, and what if there is some updates on the requested page? how proxy server will act if there is such updates?

web forms function on the principle of return of data after a submit action has been implemented on that web form page. even though both users would have invoked the same web page, the resultant that is created by pressing the submit button, is different for different user. this is a return data stream for the original web site from where the web form originates. so if the first user inputs something, this does not get stored in the cache of the proxy server. so the second user will not be able to see what the first user had typed.
imagine what would have happened if such was the case!!! every single user using a particular proxy server to fetch a login page for emails would be able to see the username of the previous user (obviously the password field would yield asterisks!!!)

all cached entries are emptied after a certain interval of time. this can be configured on the proxy server how often the cache should be flushed. so in case there is an updated version of a cached web page available on the internet, the proxy server will cache that in some interval of time thus making the new version available to the user.

I read that google stopped Web Accelerator for some reasons include security reason read this news.com.com/Google+puts+brakes+on+Accel...-1032_3-5702969.html .... I don't know if it's same like what i talked about!!! ok, can you configure the interval of looking for updates? and if you, can you configure it for each page independintly?