Because we cannot document every network in a routing table, we need to know what to do with the data if the network is not listed. Quite simply, we have a catch-all route that, in essence, says if you have gone through the routing table and cannot find a match for this destination, then send it from this particular interface to this other router and let them sort it out. If the other router does not know, it will do the same.
Basically, we are playing pass the parcel with the data in the hope that it is finally received by a routing device that actually knows where the destination network is. Remember, the TTL will be counting down at each device. If no default route has been configured, then the data is simply discarded and an error message is sent back to the originating device.
A configured default route is a form of static route. An...
