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)                 9  Usenet (Network News) and the TCP/IP Network News Transfer Protocol (NNTP)                      9  TCP/IP Network News Transfer Protocol (NNTP)

NNTP Command Extensions 1 2 3 TCP/IP World Wide Web (WWW, "The Web") and the Hypertext Transfer Protocol (HTTP)

Each time the device acting as a client in an NNTP connection sends a command, the server sends back a response. The response serves to acknowledge receipt of the command, to inform the client of the results of processing the command, and possibly to prompt for additional information. Since NNTP commands are structured and formatted in a way very similar to that of SMTP commands, I'm sure it will come as no great surprise that NNTP responses are likewise very similar to those of SMTP. In turn, SMTP responses are based on the system designed for replies in FTP.

The first line of an NNTP response consists of a three-digit numerical response code, as well as a line of descriptive text that summarizes the response. These response codes are structured so that each digit has a particular significance, which allows the client to quickly determine the status of the command to which the reply was sent. After the initial response line, depending on the reply, a number of additional response lines may follow. For example, a successful LIST command results in a 215 response code, followed by a list of newsgroups.

NNTP Command Extensions 1 2 3 TCP/IP World Wide Web (WWW, "The Web") and the Hypertext Transfer Protocol (HTTP)