When a router interface is placed in the routing process it will send out IS-IS Hello packets in order to form an IS-IS neighbourship with peering IS-IS routers over that interface.
There are instances where it is desirable to include an interface in the IS-IS routing process to distribute the IPv6 prefix among the Level-2 area, but to never form an adjacency over that interface. To disable the sending of IIH packets the interface can be made passive with the command
In 6NET, all loopback interfaces and interfaces connecting to the NREN PoP routers and LAN stub interfaces were made passive.