Please Whitelist This Site? I know everyone hates ads. But please understand that I am providing premium content for free that takes hundreds of hours of time to research and write. I don't want to go to a pay-only model like some sites, but when more and more people block ads, I end up working for free. And I have a family to support, just like you. :) If you like The TCP/IP Guide, please consider the download version. It's priced very economically and you can read all of it in a convenient format without ads. If you want to use this site for free, I'd be grateful if you could add the site to the whitelist for Adblock. To do so, just open the Adblock menu and select "Disable on tcpipguide.com". Or go to the Tools menu and select "Adblock Plus Preferences...". Then click "Add Filter..." at the bottom, and add this string: "@@||tcpipguide.com^$document". Then just click OK. Thanks for your understanding! Sincerely, Charles Kozierok Author and Publisher, The TCP/IP Guide

NOTE: Using software to mass-download the site degrades the server and is prohibited. If you want to read The TCP/IP Guide offline, please consider licensing it. Thank you.

The TCP/IP Guide  9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)       9  TCP/IP Key Applications and Application Protocols            9  TCP/IP File and Message Transfer Applications and Protocols (FTP, TFTP, Electronic Mail, USENET, HTTP/WWW, Gopher)

HTTP State Management Using "Cookies" 1 2 3 4 TCP/IP Interactive and Remote Application Protocols

Gopher Client/Server Operation

Typical use of Gopher begins with a user on a client machine creating a TCP connection to a Gopher server using well-known TCP port number 70. After the connection is established, the server waits for the client to request a particular resource by sending the server a piece of text called a selector string. Often, when a user first accesses a server, he or she does not know what resource to request, so a null (empty) selector string is sent. This causes the server to send back to the client a list of the resources available at the top (root) directory of the server’s file system tree.

A directory list sent by the server consists of a set of lines, each of which describes one available resource in that directory. Each line contains the following elements, each of which is separated by a “<Tab>” character:

• Type Character and Resource Name: The first character of the line tells the client software what sort of resource the line represents. The most common type characters are “0” for a file, “1” for a subdirectory and “7” for a search service. The rest of the characters up to the first “<Tab>” contain the name of the resource to be presented to the user.
  
  
• Selector String: The string of text to be sent to the server to retrieve this resource.
  
  
• Server Name: The name of the server where the resource is located.
  
  
• Server Port Number: The port number to be used for accessing this resource’s server; normally 70.

Each line ends with a “<CR><LF>” character sequence consistent with the Telnet Network Virtual Terminal (NVT) specification. Upon sending the directory listing (or any other response) the connection between the client and server is closed.

HTTP State Management Using "Cookies" 1 2 3 4 TCP/IP Interactive and Remote Application Protocols