IS-IS route summarization allows users to create aggregate IPv4 or IPv6 addresses that include multiple groups of IPv4 or IPv6 addresses for a specific IS-IS level. IPv4 and IPv6 routes redistributed from other routing protocols also can be summarized. This is similar to OSPF configuration using the area-range command. IS-IS IPv4 and IPv6 route summarization helps to reduce the size of the LSDB and the IPv4 or IPv6 routing table, and reduces the chance of route flapping.
IS-IS route summarization supports:
level 1, level 1-2, and level 2
route summarization for the IPv4 or IPv6 routes redistributed from other protocols
the smallest metric used to advertise summary addresses of all the more specific IPv4 or IPv6 routes
IS-IS IPv6 route summarization algorithm and SRv6 locator awareness