Web Servers Web Servers Computers which store web

Web Servers

Web Servers • Computers which store web pages in the form of directories and files and provide these files to be read, are called Server. • The server computer runs special software called web server. • Clients “connect” to the machine • Clients send a “request” • Server reads request, generates “response”

A Simplified Web Server • Client asks for file • Server finds appropriate file • Server sends back a response header followed by the requested file’s data • Server closes connection

Today Available Servers • 1. IIS: Internet Information Server, that comes free with the windows, is one of the most commonly used web server these days. IIS is the product of Microsoft. • 2. PWS: Personal Web Server is compatible with older version of MS Window.

• 3. Apache: The Apache web server is also one of the most widely used web server. This is available with each version of MS Window as well as for all Unix flavours. • It can be downloaded from the web site of apache.

Basic Types of Server 1. Database Server : - The Server which provides access to information stored at database and provides features to analyze and store the data in a network environment is called database server. A database server must have following properties: Ø It must be reliable. Ø It must provide quick access to information.

• 2. Application Server : - The application server also acts in the way as the client server model. It helps to run specific applications. • The user can not directly communicate through application server rather than communication is done via some other server working at user layer. e. g. through DNS server, mail server, web server.

Server Specification Firewall User level DNS Server Mail Server Web Server App. level Application Server External DB Server Data level File Server Internal Database Server

What Is a Proxy Server? • Intermediary server between clients and the actual server • Proxy processes request • Proxy processes response • Intranet proxy may restrict all outbound/inbound requests to the intranet server

TCP Connection Termination • Both the outgoing and incoming TCP connections are terminated • prevents a hacker from hijacking a stale connection on a service that is being proxied • ex. HTTP page request packet’ request packet User Proxy response packet Connection left open until the proxy closes it after receiving response packet and sending it back to user Server response packet’ Connection only left open until server closes the connection after sending the response packet

What Does a Proxy Server Do? ØBetween client and server ØReceives the client request ØDecides if request will go on to the server ØMay have cache & may respond from cache ØActs as the client with respect to the server ØUses one of it’s own IP addresses to get page from server

Usual Uses for Proxies • Firewalls • Employee web use control (email etc. ) • Web content filtering (kids) • Black lists (sites not allowed) • White lists (sites allowed)

User Perspective ØProxy is invisible to the client. ØIP address of proxy is the one by which browser is configured to go there. ØSpeed up retrieval if using caching. ØCan implement profiles or personalization.

Main Proxy Functions Ø Caching Ø Firewall Ø Filtering

Web Cache Proxy ØOur concern is not with browser cache! ØStore frequently used pages at proxy rather than request the server to find or create again ØWhy? ØReduce latency: faster to get from proxy & so makes the server seem more responsive ØReduce traffic: reduces traffic to actual server • Proxy cache serves hundreds/thousands of users at a time. • Most popular requests are generated only once.

• 2. Firewalls Ø Proxies uses firewalls for security or protection. Ø It provide packet filtering schemes. Ø It is not dependent on other hardware and software. • 3. Filtering at the Proxy 1. URL lists (black and white lists) Ø Black list : URLs proxy will not access Ø White list: URLs proxy will allow access

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