3.5 ICMP and Routing
nICMP is used to indicate an error condition related to routing.
nIf a solution is
feasible, i.e., a route is available,
then ICMP is used to indicate the new route to
the source, redirect message.
nIf a solution is not feasible, i.e., a route is not available, then it is used to indicate that the destination host is unreachable.