Understanding IS-IS Flood Group
IS-IS supports flood-group. This feature limits link-state packet data unit (PDU) flooding over IS-IS interfaces.
A link-state packet (LSP) that is not self-originated will be
flooded only through the interface belonging to the flood group that
has the configured area ID in the LSP. This helps minimize the routes
and topology information, thus ensuring optimal convergence. You can
segregate both Level 1 and Level 2 IS-IS routers into flood
groups by using area IDs as tags to identify a flood group. Configure
interfaces with specific area IDs to modify the flooding behavior
as per your requirements. To enable IS-IS flood group, include the flood-group flood-group-area-ID statement
at the [edit protocols isis interface] hierarchy level.