120 lines
6.4 KiB
HTML
120 lines
6.4 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
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<!--Converted with LaTeX2HTML 96.1-c (Feb 29, 1996) by Nikos Drakos (nikos@cbl.leeds.ac.uk), CBLU, University of Leeds -->
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<HTML>
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<HEAD>
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<TITLE>Introduction</TITLE>
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</HEAD>
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<BODY LANG="EN">
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<A HREF="node1.html"><IMG WIDTH=65 HEIGHT=24 ALIGN=BOTTOM ALT="contents" SRC="contents_motif.gif"></A> <BR>
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<B> Next:</B> <A HREF="node276.html">Installing the NNTP server</A>
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<B>Up:</B> <A HREF="node274.html">A Description of NNTP</A>
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<B> Previous:</B> <A HREF="node274.html">A Description of NNTP</A>
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<BR> <P>
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<H1><A NAME="SECTION0020100000">Introduction</A></H1>
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<P>
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Due to the different network transport used, NNTP provides for a vastly
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different approach to news exchange from C-news. NNTP stands for
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``Network News Transfer Protocol'', and is not a particular software
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package, but an Internet Standard.<A HREF="footnode.html#9623"><IMG ALIGN=BOTTOM ALT="gif" SRC="foot_motif.gif"></A> It is based on a stream-oriented connection-- usually over TCP--
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between a client anywhere in the network, and a server on a host that keeps
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netnews on disk storage. The stream connection allows the client and server
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to interactively negotiate article transfer with nearly no turnaround
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delay, thus keeping the number of duplicate articles low. Together with the
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Internet's high transfer rates, this adds up to a news transport that
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surpasses the original UUCP networks by far. While some years ago it was
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not uncommon for an article to take two weeks or more before it arrived in
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the last corner of Usenet, this is now often less than two days; on the
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Internet itself, it is even within the range of minutes.
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<P>
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Various commands allow clients to retrieve, send and post articles.
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The difference between sending and posting is that the latter may
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involve articles with incomplete header information.<A HREF="footnode.html#9767"><IMG ALIGN=BOTTOM ALT="gif" SRC="foot_motif.gif"></A> Article retrieval may be used by news transfer clients as well as
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newsreaders. This makes NNTP an excellent tool for providing news access to
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many clients on a local network without going through the contortions that
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are necessary when using NFS.
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<P>
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<A NAME="9625"></A>
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<A NAME="9626"></A>
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NNTP also provides for an active and a passive way of news transfer,
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colloquially called ``pushing'' and ``pulling''. Pushing is basically
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the same as the C-news ihave/sendme protocol. The client offers an
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article to the server through the ``IHAVE <varmsgid>''
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command, and the server returns a response code that indicates whether
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it already has the article, or if it wants it. If so, the client sends
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the article, terminated by a single dot on a separate line.
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<P>
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Pushing news has the single disadvantage that it places a heavy load on
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the server system, since it has to search its history database for every
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single article.
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<P>
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The opposite technique is pulling news, in which the client requests a
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list of all (available) articles from a group that have arrived after a
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specified date. This query is performed by the NEWNEWS
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command. From the returned list of message ids, the client selects those
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articles it does not yet have, using the ARTICLE command for
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each of them in turn.
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<P>
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The problem with pulling news is that it needs tight control by the server
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over which groups and distributions it allows a client to request. For
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example, it has to make sure that no confidential material from newsgroups
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local to the site are sent to unauthorized clients.
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<P>
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There are also a number of convenience commands for newsreaders that
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permit them to retrieve the article header and body separately, or even
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single header lines from a range of articles. This lets you keep all
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news on a central host, with all users on the (presumably local) network
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using NNTP-based client programs for reading and posting. This is an
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alternative to exporting the news directories via NFS which is described
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in chapter-<A HREF="node259.html#cnews"><IMG ALIGN=BOTTOM ALT="gif" SRC="cross_ref_motif.gif"></A>.
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<P>
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<A NAME="9631"></A>
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An overall problem of NNTP is that it allows the knowledgeable to insert
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articles into the news stream with false sender specification. This is
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called <em>news faking</em>.<A HREF="footnode.html#9633"><IMG ALIGN=BOTTOM ALT="gif" SRC="foot_motif.gif"></A> An extension to NNTP allows to require a user authentication for
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certain commands.
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<P>
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<A NAME="9769"></A>
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<A NAME="9635"></A>
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<A NAME="9636"></A>
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There are a number of NNTP packages available. One of the more widely known
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is the NNTP daemon, also known as the <em>reference implementation</em>.
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Originally, it was written by Stan Barber and Phil Lapsley to illustrate
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the details of RFC-977. Its most recent version is nntpd-1.5.11,
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which will be described below. You may either get the sources and compile
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it yourself, or use the nntpd from Fred van-Kempen's net-std
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binary package. No ready-to-go binaries of nntpd are provided,
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because of various site-specific values that must be compiled in.
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<P>
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The nntpd package consists of a server and two clients for
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pulling and pushing news, respectively, as well as an inews
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replacement. They live in a Bnews environment, but with a little
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tweaking, they will be happy with C-news, too. However if you plan to
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use NNTP for more than offering newsreaders access to your news server,
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the reference implementation is not really an option. We will therefore
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discuss only the NNTP daemon contained in the nntpd package, and
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leave out the client programs.
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<P>
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<A NAME="9645"></A>
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<A NAME="9646"></A>
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There is also a package called ``InterNet News'', or INN for short, that was
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written by Rich Salz. It provides both NNTP and UUCP-based news
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transport, and is more suitable for large news hubs. When it comes to
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news transport over NNTP, it is definitely better than nntpd.
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INN is currently at version inn-1.4sec. There is a kit for
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building INN on a machine from Arjan de Vet; it is available
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from sunsite.unc.edu in the system/Mail directory. If you
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want to set up INN, please refer to the documentation that comes along
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with the source, as well as the INN-FAQ posted regularly to
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news.software.b.
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<P>
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<HR><A HREF="node1.html"><IMG WIDTH=65 HEIGHT=24 ALIGN=BOTTOM ALT="contents" SRC="contents_motif.gif"></A> <BR>
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<B> Next:</B> <A HREF="node276.html">Installing the NNTP server</A>
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<B>Up:</B> <A HREF="node274.html">A Description of NNTP</A>
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<B> Previous:</B> <A HREF="node274.html">A Description of NNTP</A>
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<P><ADDRESS>
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<I>Andrew Anderson <BR>
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Thu Mar 7 23:22:06 EST 1996</I>
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</ADDRESS>
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</BODY>
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</HTML>
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