To eliminate the need for adjacent routers on broadcast networks to form n(n-1)/2 adjacencies, IS-IS defines a pseudonode or Designated Intermediate System, DIS. All router on the broadcast medium form an adjacency with the DIS. The Backup DIS is called:

A.
Redundant DIS

B.
BDR

C.
There is no concept of a backup DIS in IS-IS

D.
Designated Redundant System