A router is a network device that is used to connect two different
    networks together.  The difference in the networks can be as trivial
    as that they are on different subnets, or complex as in
    connecting and translating a DSL line to a local LAN, for example.
    A router can be a separate device as in a Cisco router or a router
    can be a computer with 2 network cards.  A firewall is a router that
    only allows specific traffic to pass between networks.

A router can be a separate device as in a Cisco router or a router can be a computer with 2 network cards. A firewall is a router that only allows specific traffic to pass between networks.

Static Route:

    When a computer on network A needs to talk to a computer on network B,
    the data passes out through network A's router that is also connected
    to network B.  The router between network A and network B needs to be
    told that traffic destined for B exits the router through B's ethernet
    card.  When you specify that, you specify a static route from A to B.
    You also need to tell the router that traffic destined for A exits the
    router on A's NIC.  So you need two static routes on the router between
    A and B.  These static routes get created automatically by scoadmin netw.

Default Route:

    The default route sends all traffic without a static route out through
    the default gateway.  So all traffic has some route to go through.
    Once again we have network A connected to network B through a router,
    and network B connected to network C through a different router.  When
    a host on A wants to talk to a host on C, we could specify a static route,
    but that quickly becomes rediculous when we consider having to specify
    static routes to google, caldera, ibm, sourceforge, etc.  Instead we use
    a default route, rather than many static routes.  The default route is
    the fall back.  It says to a router that if you don't have a path
    specified to get traffic from A to C, then just send the traffic out
    the default route.

If there is no static route from A to B, then the system will fall back onto the default route to get data out to an unknown IP network. Because our computers are generally attached to only one subnet, and because there is usually a router on that subnet to connect that subnet to the rest of the world, the host in this case always uses the same route to get its data out. That route is what we want to use as the default route.

When a computer on network A needs to talk to a computer on network B, the data passes back and forth through the router, using it as the connection between the networks. The path that the data takes from network A to B through the router is called a route. For computers on A to talk to B, they need to have a route entered in their Operating System's routing table. In the routing table, a route is listed as the IP address of the router. This says to the host, use the router as the route to any unknown IP.

If there is no static route from A to B, then the system will fall back onto the default route to get data out to an unknown IP network. Because our computers are generally attached to only one subnet, and because there is usually a router on that subnet to connect that subnet to the rest of the world, the host in this case always uses the same route to get its data out. That route is what we want to use as the default route.

<mschalit@pacbell.net>