Refer to the exhibit. A network engineer notices PE-21 convergence degradation due to the growing LSDB size of Level 2 areas in the network. The engineer decides to migrate router PE-21 from an…

This configuration does not explicitly set `is-type level-1` and instead uses `ip router isis` on the interface, which is not the correct approach for defining the IS-IS type at the global router level. Without `is-type level-1`, it defaults to `level-1-2`, contradicting the goal.

This configuration attempts to set `level-1` but uses an incorrect `network` command syntax for defining the Area ID and doesn't correctly set the `is-type` under the IS-IS process, which is critical for the migration.

Configuring PE-21 as `is-type level-1-2` means it would continue to carry both Level 1 and Level 2 LSDBs, directly opposing the objective of reducing the LSDB size by migrating to an intra-area (Level 1 only) implementation.

Configuring PE-21 with `is-type level-1` explicitly designates it as a Level 1 only router, which prevents it from maintaining a Level 2 LSDB and significantly reduces its overall LSDB size, addressing the convergence degradation. The `net 49.0001.0000.0000.0021.00` command correctly assigns its System ID and associates it with IS-IS area 0.0001, allowing it to forward inter-area traffic using the ATT bit set by Level 1/Level 2 routers.