What is a stub network?

Concept: In internetworking, a network segment's routing needs are determined by how many independent connections it has to the rest of the internetwork. A network with exactly one such connection is called a stub network: since there is only one link in and out, every packet leaving or entering that segment must use that same link, so a single default route is enough, and dynamic routing protocols -- which exist to choose among multiple paths -- add no value.

Application: The definition being asked for must therefore describe a network with exactly one connection point, i.e. one entry and one exit -- matching the option describing a network that has only one entry and exit point.

Cross-check — why the other descriptions don't fit:

• A network with more than one exit point describes multiple independent paths out, making it a transit network that needs to choose among routes, not a stub network.

• A network with more than one exit and entry point is the same idea from both directions -- multiple entry/exit pairs are the hallmark of a backbone or transit network running dynamic routing, not a stub network.

• A network with only one entry and no exit point is internally inconsistent: a segment that can only receive but never send or forward traffic back out has no way to route anything, so it does not correspond to any real network's connectivity.

Result: A stub network is exactly the network with one entry and one exit point -- a single connection to the internetwork.