You can enable the device to advertise a default route to all neighboring ISs. The following task enables the advertisement of a default route.
device# configure terminal
device(config)# router isis
device(config-isis-router)# address-family ipv6 unicast
device(config-router-isis-ipv6u)# default-information-originate
The following example enables the advertisement of a default route for the IS-IS IPv6 unicast address-family.
device# configure terminal device(config)# router isis device(config-isis-router)# address-family ipv6 unicast device(config-router-isis-ipv6u)# default-information-originate