A network has several routers running IS-IS Layer 1/Layer 2 mode on the same Ethernet segment. Which action reduces the number of the IS-IS adjacencies to a minimum in this segment?

The DIS priority determines which router becomes the elected DIS, but in IS-IS all routers on a broadcast segment still form adjacencies with every other router regardless of DIS role - lowering the backup DIS priority does not reduce the number of adjacencies.

When all routers on a segment operate in the same single level (either all L1 or all L2), each router pair forms only one IS-IS adjacency instead of two (one per level). L1/L2 mode causes every router to maintain both a Level 1 and a Level 2 adjacency with every other L1/L2 router on the segment, so removing the dual-level configuration is the most effective way to minimize total adjacency count.

Unlike OSPF, IS-IS does not restrict adjacency formation to only the DIS; all routers on a broadcast segment form full adjacencies with each other, so having only one DIS elected does not reduce the total adjacency count.

Splitting routers into L1-only and L2-only groups prevents cross-level adjacency formation but creates two isolated sets and does not minimize overall adjacencies across the segment compared to a single unified level.