The following commands enable IPv6 IS-IS MT on device C2.
device# configure terminal device(config)# router isis device(config-isis-router)# net 00.0000.001b.ed04.0000.00 device(config-isis-router)# address-family ipv4 unicast device(config-router-isis-ipv4u)# metric-style wide device(config-router-isis-ipv4u)# exit device(config-isis-router)# address-family ipv6 unicast device(config-router-isis-ipv6u)# multi-topology device(config-router-isis-ipv6u)# exit