Dell PowerEdge FN I/O Module Configuration Guide 9.10(0.0)

If a local router does not participate in certain MTs, it does not advertise those MT IDs in its IS-IS hellos (IIHs) and so does not include that neighbor within its LSPs. If an MT ID is not detected in the remote side’s IIHs, the local router does not include that neighbor within its LSPs. The local router does not form an adjacency if both routers do not have at least one common MT over the interface.