Due to the different network transport used, NNTP provides for a vastly
different approach to news exchange from C-news. NNTP stands for
``Network News Transfer Protocol'', and is not a particular software
package, but an Internet Standard.
It is based on a stream-oriented connection-- usually over TCP--
between a client anywhere in the network, and a server on a host that keeps
netnews on disk storage. The stream connection allows the client and server
to interactively negotiate article transfer with nearly no turnaround
delay, thus keeping the number of duplicate articles low. Together with the
Internet's high transfer rates, this adds up to a news transport that
surpasses the original UUCP networks by far. While some years ago it was
not uncommon for an article to take two weeks or more before it arrived in
the last corner of Usenet, this is now often less than two days; on the
Internet itself, it is even within the range of minutes.
Various commands allow clients to retrieve, send and post articles.
The difference between sending and posting is that the latter may
involve articles with incomplete header information. Article retrieval may be used by news transfer clients as well as
newsreaders. This makes NNTP an excellent tool for providing news access to
many clients on a local network without going through the contortions that
are necessary when using NFS.
NNTP also provides for an active and a passive way of news transfer, colloquially called ``pushing'' and ``pulling''. Pushing is basically the same as the C-news ihave/sendme protocol. The client offers an article to the server through the ``IHAVE <varmsgid>'' command, and the server returns a response code that indicates whether it already has the article, or if it wants it. If so, the client sends the article, terminated by a single dot on a separate line.
Pushing news has the single disadvantage that it places a heavy load on the server system, since it has to search its history database for every single article.
The opposite technique is pulling news, in which the client requests a list of all (available) articles from a group that have arrived after a specified date. This query is performed by the NEWNEWS command. From the returned list of message ids, the client selects those articles it does not yet have, using the ARTICLE command for each of them in turn.
The problem with pulling news is that it needs tight control by the server over which groups and distributions it allows a client to request. For example, it has to make sure that no confidential material from newsgroups local to the site are sent to unauthorized clients.
There are also a number of convenience commands for newsreaders that
permit them to retrieve the article header and body separately, or even
single header lines from a range of articles. This lets you keep all
news on a central host, with all users on the (presumably local) network
using NNTP-based client programs for reading and posting. This is an
alternative to exporting the news directories via NFS which is described
in chapter-
.
An overall problem of NNTP is that it allows the knowledgeable to insert
articles into the news stream with false sender specification. This is
called news faking. An extension to NNTP allows to require a user authentication for
certain commands.
There are a number of NNTP packages available. One of the more widely known is the NNTP daemon, also known as the reference implementation. Originally, it was written by Stan Barber and Phil Lapsley to illustrate the details of RFC-977. Its most recent version is nntpd-1.5.11, which will be described below. You may either get the sources and compile it yourself, or use the nntpd from Fred van-Kempen's net-std binary package. No ready-to-go binaries of nntpd are provided, because of various site-specific values that must be compiled in.
The nntpd package consists of a server and two clients for pulling and pushing news, respectively, as well as an inews replacement. They live in a Bnews environment, but with a little tweaking, they will be happy with C-news, too. However if you plan to use NNTP for more than offering newsreaders access to your news server, the reference implementation is not really an option. We will therefore discuss only the NNTP daemon contained in the nntpd package, and leave out the client programs.
There is also a package called ``InterNet News'', or INN for short, that was written by Rich Salz. It provides both NNTP and UUCP-based news transport, and is more suitable for large news hubs. When it comes to news transport over NNTP, it is definitely better than nntpd. INN is currently at version inn-1.4sec. There is a kit for building INN on a machine from Arjan de Vet; it is available from sunsite.unc.edu in the system/Mail directory. If you want to set up INN, please refer to the documentation that comes along with the source, as well as the INN-FAQ posted regularly to news.software.b.