90 lines
4.4 KiB
HTML
90 lines
4.4 KiB
HTML
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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>Mail Routing in the UUCP World</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="node193.html">Mixing UUCP and RFC-822</A>
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<B>Up:</B> <A HREF="node190.html">How does Mail Routing </A>
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<B> Previous:</B> <A HREF="node191.html">Mail Routing on the </A>
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<BR> <P>
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<H2><A NAME="SECTION0015420000">Mail Routing in the UUCP World</A></H2>
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<A NAME="mailroutinguucp"></A>
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Mail routing on UUCP networks is much more complicated than on the
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Internet, because the transport software does not perform any routing
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itself. In earlier times, all mail had to be addressed using bang paths.
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Bang paths specified a list of hosts through which to forward the
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message, separated by exclamation marks, and followed by the user's
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name. To address a letter to Janet User on a machine named moria,
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you would have used the path eek!swim!moria!janet. Whis would
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have sent the mail from your host to eek, from there on to
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swim and finally to moria.
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<P>
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The obvious drawback of this technique is that it requires you to
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remember much about the network topology, fast links, etc. Much worse
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than that, changes in the network topology--- like links being deleted
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or hosts being removed--- may cause messages to fail simply because you
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weren't aware of the change. And finally, in case you move to a
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different place, you will most likely have to update all these routes.
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<P>
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One thing, however, that made the use of source routing necessary was
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the presence of ambiguous hostnames: For instance, assume there are two
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sites named moria, one in the U.S., and one in France. Which site
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now does moria!janet refer to? This can be made clear by
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specifying what path to reach moria through.
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<P>
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The first step in disambiguating hostnames was the founding of
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<em>The UUCP Mapping Project</em>. It is located at Rutgers University, and
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registers all official UUCP hostnames, along with information on their
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UUCP neighbors and their geographic location, making sure no hostname is
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used twice. The information gathered by the Mapping Project is published
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as the <em>Usenet Maps</em>, which are distributed regularly through
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Usenet.<A HREF="footnode.html#7166"><IMG ALIGN=BOTTOM ALT="gif" SRC="foot_motif.gif"></A> A typical system entry in a Map (after removing the comments) looks
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like this.
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<PRE>
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moria
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bert(DAILY/2),
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swim(WEEKLY)
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</PRE>
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This entry says that moria has a link to bert, which it
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calls twice a day, and swim, which it calls weekly. We will
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come back to the Map file format in more detail below.
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<P>
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Using the connectivity information provided in the maps, you can
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automatically generate the full paths from your host to any destination
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site. This information is usually stored in the paths file,
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also called <em>pathalias database</em> sometimes. Assume the Maps
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state that you can reach bert through ernie, then a
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pathalias entry for moria generated from the Map snippet above
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may look like this:
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<PRE>
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moria ernie!bert!moria!%s
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</PRE>
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If you now give a destination address of janet@moria.uucp,
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your MTA will pick the route shown above, and send the message to
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ernie with an envelope address of bert!moria!janet.
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<P>
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Building a paths file from the full Usenet maps is however not
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a very good idea. The information provided in them is usually rather
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distorted, and occasionally out of date. Therefore, only a number of
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major hosts use the complete UUCP world maps to build their
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paths file. Most sites only maintain routing information for
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sites in their neighborhood, and send any mail to sites they don't
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find in their databases to a smarter host with more complete routing
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information. This scheme is called <em>smart-host routing</em>. Hosts
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that have only one UUCP mail link (so-called <em>leaf sites</em>) don't
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do any routing of their own; they rely entirely on their smart-host.
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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="node193.html">Mixing UUCP and RFC-822</A>
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<B>Up:</B> <A HREF="node190.html">How does Mail Routing </A>
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<B> Previous:</B> <A HREF="node191.html">Mail Routing on the </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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