Of the available choices, the overload bit would be set on a router running Intermediate System to Intermediate System (IS-IS) that has recently been reloaded.

Routers that use a linkstate routing protocol maintain a complete topology of the network by flooding the state of each router's links across the entire network until each of the routers has information about all of the other routers in the autonomous system (AS). IS-IS uses Data Link layer multicast addresses to send hello packets and linkstate information. Once a recently reloaded router comes back online, if the overload bit is not set, the adjacent routers will begin forwarding packets to the router before the router can completely populate its routing table. Because the routing table is not complete, the router will drop packets to destinations that have not been written in the table yet? this describes a blackhole issue.

Multiple routes to the same destination existing on a router running IS-IS would not cause the overload bit to be set. Multiple routes typically do not exist in a routing table? however, when a network is using shortest path first (SPF), multiple routes can exist. Linkstate routing protocols consider the links that represent the shortest path to a destination as the best paths. After a router has collected linkstate information for every destination in a topology, the router uses an SPF algorithm to construct an SPF tree. The best paths from the SPF tree are then inserted into the router's routing table.

A router going offline or coming online for the first time would not cause the overload bit to be set. When a router is offline, the adjacent routers will not attempt to send packets to that router. An alternate path, if one exists, will be used to deliver packets to a destination? otherwise, the packet will be returned to the originator as undeliverable. A router coming online for the first time does not have the configuration required for the overload bit to be set.