Network News Transfer Protocol (NNTP) provides for a vastly different
approach to news exchange from C News and other news servers without native
NNTP support. Rather than rely on a batch technology like UUCP to transfer
news articles between machines, it allows articles to be exchanged via an
interactive network connection. NNTP is not a particular software package,
but an Internet standard described in RFC-977. 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; it 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; it generally means that the user has just
written the article.[1]
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 to transfer news,
colloquially called “pushing” and “pulling.” Pushing
is basically the same as the ihave/sendme protocol used by C News (described in
Chapter 21). The client offers an article to the server
through the IHAVE msgid
command, and the server returns a response code that indicates whether
it already has the article or if it wants it. If the server wants the
article, 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 the system 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.
Pulling news 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 is 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, as described
in Chapter 21.
An overall problem of NNTP is that it allows a knowledgeable person to insert
articles into the news stream with false sender specification. This is
called news faking or
spoofing.[2]
An extension to NNTP allows you to require user authentication for
certain commands, providing some measure of protection against people abusing
your news server in this way.
There are a number of NNTP packages. 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. As with much of the good software available today, you may
find it prepackaged for your Linux distribution, or you can obtain the source
and compile it yourself. If you choose to compile it yourself, you will need to
be quite familiar with your distribution to ensure you configure all of the
file paths correctly.
The nntpd package has a server, two clients for
pulling and pushing news, and an inews
replacement. They live in a B News 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.
If you wish to run a large news site, you should look at
the InterNet News package, or INN, that was written by
Rich Salz. It provides both NNTP and UUCP-based news transport. News transport is definitely better than
nntpd. We discuss INN in detail in
Chapter 23.
