Company XYZ is designing the IS-IS deployment strategy for their multiarea IS-IS domain. They want IS-IS neighbor relationships to be minimized on each network segment and want to optimize the size…

Making all routers Level 2 means every router must maintain full domain-wide topology in the L2 LSDB, which maximizes LSDB size across all routers rather than optimizing it.

Using only Level 2 routers at area borders without Level 1 internal routers does not partition the LSDB - internal routers would still need L2 adjacencies and carry full domain topology, defeating the goal of LSDB optimization.

All Level 1 routers cannot exchange routing information between areas because inter-area reachability requires L2 adjacencies, making a multiarea IS-IS domain non-functional with this design.

In IS-IS, Level 1/Level 2 routers at area boundaries maintain both the L1 LSDB for their local area and the L2 LSDB for inter-area routing, while purely Level 1 internal routers maintain only their smaller local area LSDB. This hierarchy limits the number of adjacency types each internal router must form and prevents full domain topology from flooding into every router, satisfying both the adjacency minimization and LSDB optimization requirements.