Internetworking Servers
In a Nutshell - CIW Course Section 1, Part C, Chapter 6
In this chapter we shall look at some of the server types you are likely to encounter on the Internet when configuring your web sites.
HTTP Server Essentials
The World Wide Web is a collection of computer systems running the HTTP service. These servers act together as document delivery systems. Documents are delivered to systems running Web browsers, also called clients.
The Web operates on a TCP/IP application-layer protocol known as HTTP. The HTTP server and the Web browser are examples of client/server communications. Worldwide interaction between the two also exemplifies the hyper-distributed networking involved in Web-based networking.
HTTP Servers
An HTTP server can download any file type. Although a Web browser renders only certain types of images, HTTP can process a variety of situations. The Multipurpose Internet Mail Extensions (MIME) system allows HTTP and e-mail attachments to identify the files they must use. The different MIME types are classified under broad headings (text, image, application, audio and video), then sub-classified by exact type. For example, an HTML document has MIME type "text/html", whereas a plain text file has type "text/plain".
Proxy Servers
A proxy server is an intermediary between a network host and other hosts outside the network. Its main functions are to provide enhanced security, manage TCP/IP addresses, and speed access to the Internet by caching server functions for frequently used documents.
Proxy Servers can provide the following additional services:
- Caching of web documents - When a document (web page) is retrieved from the Intenet it is delivered to the client and also stored locally on the proxy server, so that subsequent requests can be met from the proxy rather having to go back out to the Internet. This speeds document access and reduces bandwidth usage,
- Corporate firewall access - This allows safe access for corporate users out to the Internet and prevents unauthorised users gaining access to the corporate network from outside.
- Filtering client transactions - This can allow or deny access to specific URLs, optionally diverting the request to an alternate web page.
- Transaction logging - Can log the users accessing the Internet, which pages are requested and the amount of data retrieved.
- Securing the host - This is similar to the firewall role
Mail Servers
A mail server stores and forwards e-mail messages using several protocols including SMTP, POP and IMAP. SMTP is used solely for sending messages, POP3 is used for retrieving messages. IMAP handles messages in a more sophisticated way allowing a user to browse and manage files remotely, whereas POP3 server forces the user to download files.
Media Servers
A media server offers streaming audio and video over a network. These severs are useful because businesses and other organisations use the Internet to conduct long-distance conference calls as personally as possible. Generally, these servers use UDP ports and buffering to achieve the effect of a real-time connection.
DNS Servers
Invented in 1984 by Paul Mockapetris, the Domain Name System (DNS) is a mechanism used on the Internet to translate host computer names into IP addresses.
DNS consists of two key components:
- Name Server - a server that supports name-to-address translation and runs the DNS service.
- Name Resolver - software that uses the services of one or more name servers to resolve an unknown request.
FTP Servers
Even though File Transfer Protocol (FTP) is one of the oldest protocols in use on the Internet, it still remains the workhorse of many servers and administrators. FTP is used to transfer text and binary files. These files are stored on the FTP server and are accessed by an FTP client for either download or upload. Files may be transferred by HTTP or SMTP, but neither can match the speed or reliability of FTP. Only FTP can upload files.
Certificate Servers
Certificate Servers validate, or certify, keys. Keys are strings of text generated from a complex series of encryption algorithms that allow you to secure communications for a company or group of users.
A certificate server generates and manages digital certificates by using cryptography. In the context of messaging, cryptography takes two forms: encryption and digital signatures.