This indicates which type of packets will be sent and accepted on this circuit, with the values used modified by the settings of ciiSysType, and it follows the replaceOnlyWhileDisabled behavior. It is the per-circuit counterpart to the router-wide ciiSysType, letting an admin run level1 only on an access-facing interface while running level2 or both on a core-facing interface of the same L1L2 router, though the effective levels are still constrained by whatever ciiSysType allows system-wide. For example, on an L1L2 border router an admin might set this to level1 on interfaces facing access switches and level2 on the interface facing the backbone, keeping backbone LSP flooding off the access-facing links entirely.