429 lines
9.6 KiB
HTML
429 lines
9.6 KiB
HTML
<HTML
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>NNTP and thenntpd Daemon</TITLE
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WIDTH="100%"></DIV
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><DIV
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CLASS="CHAPTER"
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><H1
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><A
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NAME="X-087-2-NNTP"
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>Chapter 22. NNTP and thenntpd Daemon</A
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></H1
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><DIV
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CLASS="TOC"
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><DL
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><DT
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><B
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>Table of Contents</B
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></DT
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><DT
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>22.1. <A
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HREF="x-087-2-nntp.protocol.html"
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>The NNTP Protocol</A
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></DT
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><DD
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><DL
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><DT
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>22.1.1. <A
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HREF="x-087-2-nntp.protocol.html#AEN17812"
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>Connecting to the News Server</A
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></DT
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><DT
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>22.1.2. <A
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HREF="x-087-2-nntp.protocol.html#AEN17825"
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>Pushing a News Article onto a Server</A
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></DT
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><DT
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>22.1.3. <A
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HREF="x-087-2-nntp.protocol.html#AEN17849"
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>Changing to NNRP Reader Mode</A
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></DT
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><DT
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>22.1.4. <A
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HREF="x-087-2-nntp.protocol.html#AEN17863"
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>Listing Available Groups</A
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></DT
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><DT
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>22.1.5. <A
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HREF="x-087-2-nntp.protocol.html#AEN17880"
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>Listing Active Groups</A
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></DT
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><DT
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>22.1.6. <A
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HREF="x-087-2-nntp.protocol.html#AEN17892"
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>Posting an Article</A
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></DT
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><DT
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>22.1.7. <A
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HREF="x-087-2-nntp.protocol.html#AEN17912"
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>Listing New Articles</A
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></DT
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><DT
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>22.1.8. <A
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HREF="x-087-2-nntp.protocol.html#AEN17932"
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>Selecting a Group on Which to Operate</A
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></DT
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><DT
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>22.1.9. <A
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HREF="x-087-2-nntp.protocol.html#AEN17948"
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>Listing Articles in a Group</A
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></DT
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><DT
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>22.1.10. <A
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HREF="x-087-2-nntp.protocol.html#AEN17962"
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>Retrieving an Article Header Only</A
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></DT
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><DT
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>22.1.11. <A
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HREF="x-087-2-nntp.protocol.html#AEN17982"
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>Retrieving an Article Body Only</A
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></DT
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><DT
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>22.1.12. <A
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HREF="x-087-2-nntp.protocol.html#AEN17994"
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>Reading an Article from a Group</A
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></DT
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></DL
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></DD
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><DT
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>22.2. <A
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HREF="x-087-2-nntp.nntpd.html"
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>Installing the NNTP Server</A
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></DT
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><DT
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>22.3. <A
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HREF="x-087-2-nntp.access.html"
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>Restricting NNTP Access</A
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></DT
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><DT
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>22.4. <A
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HREF="x-087-2-nntp.authorize.html"
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>NNTP Authorization</A
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></DT
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><DT
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>22.5. <A
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HREF="x-087-2-nntp.interact.html"
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>nntpd Interaction with C News</A
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></DT
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></DL
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></DIV
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><P
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>Network News Transfer Protocol (NNTP) provides for a vastly different
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approach to news exchange from C News and other news servers without native
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NNTP support. Rather than rely on a batch technology like UUCP to transfer
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news articles between machines, it allows articles to be exchanged via an
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interactive network connection. NNTP is not a particular software package,
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but an Internet standard described in RFC-977. It is based on a
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stream-oriented connection, usually over TCP, between a client anywhere in
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the network and a server on a host that keeps Netnews on disk storage. The
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stream connection allows the client and server to interactively negotiate
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article transfer with nearly no turnaround delay, thus keeping the number of
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duplicate articles low. Together with the Internet's high-transfer rates,
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this adds up to a news transport that surpasses the original UUCP networks by
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far. While some years ago it was not uncommon for an article to take two
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weeks or more before it arrived in the last corner of Usenet; it is now often
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less than two days. On the Internet itself, it is even within the range of
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minutes.</P
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><P
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>Various commands allow clients to retrieve, send, and post articles. The
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difference between sending and posting is that the latter may involve articles
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with incomplete header information; it generally means that the user has just
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written the article.<A
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NAME="X-087-2-FNNN01"
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HREF="#FTN.X-087-2-FNNN01"
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>[1]</A
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>
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Article retrieval may be used by news transfer clients as well as newsreaders.
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This makes NNTP an excellent tool for providing news access to many clients on
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a local network without going through the contortions that are necessary when
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using NFS.</P
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><P
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>
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NNTP also provides for an active and a passive way to transfer news,
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colloquially called “pushing” and “pulling.” Pushing
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is basically the same as the ihave/sendme protocol used by C News (described in
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<A
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HREF="x-087-2-cnews.html"
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>Chapter 21</A
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>). The client offers an article to the server
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through the <B
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CLASS="COMMAND"
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>IHAVE msgid</B
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>
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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 the server wants the
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article, the client sends the article, terminated by a single dot on a
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separate line.</P
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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 the system has to search its history database for
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every single article.</P
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><P
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>
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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
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<B
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CLASS="COMMAND"
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>NEWNEWS</B
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> command. From the returned
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list of message IDs, the client selects those articles it does not yet have,
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using the <B
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CLASS="COMMAND"
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>ARTICLE</B
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> command for
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each of them in turn.</P
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><P
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>Pulling news needs tight control by the server over which groups and
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distributions it allows a client to request. For example, it has to make
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sure that no confidential material from newsgroups local to the site is sent
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to unauthorized clients.</P
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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, as described
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in <A
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HREF="x-087-2-cnews.html"
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>Chapter 21</A
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>.</P
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><P
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>
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An overall problem of NNTP is that it allows a knowledgeable person to insert
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articles into the news stream with false sender specification. This is
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called <I
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CLASS="EMPHASIS"
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>news faking</I
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> or
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<I
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CLASS="EMPHASIS"
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>spoofing</I
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>.<A
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NAME="X-087-2-FNNN02"
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HREF="#FTN.X-087-2-FNNN02"
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>[2]</A
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>
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An extension to NNTP allows you to require user authentication for
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certain commands, providing some measure of protection against people abusing
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your news server in this way.</P
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><P
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>
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There are a number of NNTP packages. One of the more widely known is
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the NNTP daemon, also known as the
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<I
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CLASS="EMPHASIS"
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>reference implementation</I
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>.
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Originally, it was written by Stan Barber and Phil Lapsley to illustrate the
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details of RFC-977. As with much of the good software available today, you may
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find it prepackaged for your Linux distribution, or you can obtain the source
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and compile it yourself. If you choose to compile it yourself, you will need to
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be quite familiar with your distribution to ensure you configure all of the
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file paths correctly.</P
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><P
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>The <B
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CLASS="COMMAND"
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>nntpd</B
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> package has a server, two clients for
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pulling and pushing news, and an <B
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CLASS="COMMAND"
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>inews</B
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>
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replacement. They live in a B News 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 <B
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CLASS="COMMAND"
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>nntpd</B
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> package
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and leave out the client programs.</P
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><P
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>
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If you wish to run a large news site, you should look at
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the <I
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CLASS="EMPHASIS"
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>InterNet News</I
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> package, or INN, that was written by
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Rich Salz. It provides both NNTP and UUCP-based news transport. News transport is definitely better than
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<B
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CLASS="COMMAND"
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>nntpd</B
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>. We discuss INN in detail in
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<A
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HREF="x-087-2-inn.html"
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>Chapter 23</A
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>.</P
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></DIV
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><H3
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CLASS="FOOTNOTES"
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>Notes</H3
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><TABLE
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BORDER="0"
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WIDTH="100%"
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><TR
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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WIDTH="5%"
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><A
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NAME="FTN.X-087-2-FNNN01"
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HREF="x-087-2-nntp.html#X-087-2-FNNN01"
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>[1]</A
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></TD
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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WIDTH="95%"
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><P
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> When posting an
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article over NNTP, the server always adds at least one header field, <TT
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CLASS="LITERAL"
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>NNTP-Posting-Host:</TT
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>. The field contains the client's hostname.</P
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></TD
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></TR
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><TR
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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WIDTH="5%"
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><A
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NAME="FTN.X-087-2-FNNN02"
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HREF="x-087-2-nntp.html#X-087-2-FNNN02"
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>[2]</A
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></TD
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><TD
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ALIGN="LEFT"
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VALIGN="TOP"
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WIDTH="95%"
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><P
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>The same problem exists with the Simple Mail Transfer Protocol (SMTP), although
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most mail transport agents now provide mechanisms to prevent spoofing.</P
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></TD
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></TR
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>Maintenance Tools and Tasks</TD
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