A node also maintains a repository of all nodes reachable via symmetric neighbors. This is the two hop neighbor set. This database is used for MPR calculation.
Upon receiving a HELLO message from a symmetric neighbor, all reported symmetric neighbors, not including addresses belonging to the local node, are added or updated in the two hop neighbor set. Entries in the two hop neighbor set are all based on main addresses, so for all received entries in the HELLO message the MID set is queried for the main address. Note that the two hop neighbors also may contain neighbors reachable by one hop.