A network has several routers running IS-IS L1L2 mode on the same Ethernet segment. Which action reduces to a minimum the number of IS-IS adjacencies in this segment?

Unlike OSPF where only DR/BDR relationships are fully established, IS-IS routers on a broadcast segment form adjacencies with all other routers regardless of which router is elected DIS, so changing DIS assignment has no effect on adjacency count.

When multiple L1L2 routers share an Ethernet segment, each router pair maintains two separate adjacencies - one for L1 and one for L2 - because IS-IS broadcast segments require full adjacency between all routers, not just with the DIS. Converting all routers to a single IS-IS level (all L1 or all L2) eliminates the dual adjacency requirement, reducing the total adjacency count by half and achieving the minimum possible for that segment.

Adjusting DIS interface priority only influences which router wins the DIS election; it has no bearing on the number of adjacencies established between routers on the segment.

Splitting routers into L1-only and L2-only prevents them from forming any adjacencies with each other since they operate in incompatible levels, which would create routing partitioning and loss of reachability rather than simply reducing adjacency count.