NNTP Overview and General Operation
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Overview of NNTP Operation
The general operation of NNTP is indeed very similar to that of SMTP. NNTP uses TCP, with servers listening on well-known TCP port 119 for incoming connections, either from client hosts or other NNTP servers. As in SMTP, when two servers communicate using NNTP, the one that initiates the connection plays the role of client for that exchange.
After a connection is established, communication takes the form of commands sent by the client to the server, and replies returned from the server to the client device. NNTP commands are sent as plain ASCII text, just like those used by SMTP, FTP, HTTP and other protocols. NNTP responses take the form of three-digit reply codes as well as descriptive text, again just like SMTP (which in turn borrowed this concept from FTP).
NNTP was designed to be a comprehensive vehicle for transporting Usenet messages. It is usually most often considered as a delivery protocol for moving Usenet articles from one server to another, but is also used for connections from client hosts to Usenet servers for posting and reading messages. Thus, the NNTP command set is quite extensive, and includes commands to handle both inter-server and client-server communication. For message propagation, a set of commands is provided to allow a server to request new articles from another server, or to provide new articles to another server. For message posting and access, commands allow a client to request lists of new newsgroups and messages, and to retrieve messages for display to a user.
The commands defined in RFC 977 were the only official ones for over a decade. However, even as early as the late 1980s, implementors of NNTP server and client software were adding new commands and features to make NNTP both more efficient and useful to users. These NNTP extensions were eventually documented in RFC 2980, published in 2000. I describe them in more detail later in this section.
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