The pathalias database provides the main routing information in UUCP-based networks. A typical entry looks like this (site name and path are separated by TABs):
This makes any message to moria be delivered via ernie and bert. Both moria's fully qualified name and its UUCP name have to be given if the mailer does not have a separate way to map between these name spaces.
If you want to direct all messages to hosts inside some domain to its mail relay, you may also specify a path in the pathalias database, giving the domain name as target, preceded by a dot. For example, if all hosts in the sub.org may be reached through swim!smurf, the pathalias entry might look like this:
Writing a pathalias file is acceptable only when you are running a site that does not have to do much routing. If you have to do routing for a large number of hosts, a better way is to use the pathalias command to create the file from map files. Maps can be maintained much easier, because you may simply add or remove a system by editing the system's map entry, and re-create the map file. Although the maps published by the Usenet Mapping Project aren't used for routing very much anymore, smaller UUCP networks may provide routing information in their own set of maps.
A map file mainly consists of a list of sites, listing the sites each system polls or is polled by. The system name begins in column one, and is followed by a comma-separated list of links. The list may be continued across newlines if the next line begins with a tab. Each link consists of the name of the site, followed by a cost given in brackets. The cost is an arithmetic expression, made up of numbers and symbolic costs. Lines beginning with a hash sign are ignored.
As an example, consider moria, which polls swim.twobirds.com twice a day, and bert.sesame.com once per week. Moreover, the link to bert only uses a slow 2400bps modem. moria's would publish the following maps entry:
The last line would make it known under its UUCP name, too. Note that it must be DAILY/2, because calling twice a day actually halves the cost for this link.
Using the information from such map files, pathalias is able to calculate optimal routes to any destination site listed in the paths file, and produce a pathalias database from this which can then be used for routing to these sites.
pathalias provides a couple of other features like site-hiding (i.e. making sites accessible only through a gateway) etc. See the manual page for pathalias for details, as well as a complete list of link costs.
Comments in the map file generally contain additional information on the sites described in it. There is a rigid format in which to specify this, so that it can be retrieved from the maps. For instance, a program called uuwho uses a database created from the map files to display this information in a nicely formatted way.
When you register your site with an organization that distributes map files to its members, you generally have to fill out such a map entry.
Below is a sample map entry (in fact, it's the one for my site):
The white space after the first two characters is a TAB. The meaning of most of the fields is pretty obvious; you will receive a detailed description from whichever domain you register with. The L field is the most fun to find out: it gives your geographical position in latitude/longitude and is used to draw the postscript maps that show all sites for each country, as well as world-wide.