Having covered the first step in any network operation—finding out the address for the desired host—it is now time to turn to the second prerequisite: determining how to get there. The routing needs of many sites can be handled by installing routers and setting up default gateways and static routes on client systems (as we saw in Section 5.2). However, some situations call for more sophisticated routing services. This section provides an introduction to the daemons that provide them. The processes and algorithms described here are also used by dedicated routers.
Routing daemons dynamically select the best route from among the multiple paths to a given packet’s destination. More precisely, what is determined is the best next step along the path toward the destination, because the ultimate target may be far beyond their field of vision.
Routers cache routing information that they learn in the course of their operation, and the routers and daemons within a network use various schemes to exchange routing information.
There are two routing daemons provided by Unix systems:
routed (pronounced “route-D”) is the older and
simpler of the two and is infrequently used these days.
gated (pronounced “gate-D”) is a general
purpose routing daemon, and it is the preferred choice for most
For detailed information about the topics and daemons discussed in this section, see TCP-IP Network Administration by Craig Hunt (O’Reilly & Associates).