This read-only Counter reports the number of times this node sent an ICMP destination-unreachable message because of a source route that wasn't usable. An admin supporting source-routed traffic through this node would monitor this counter to catch cases where this node had to reject packets carrying an invalid source route. For example, a rise in cnticmpOutDuSources would indicate senders are specifying source routes that no longer correspond to valid paths through this node.