Many enterprises use OSPF version 2 for their internal IPv4 ... [database-summary | internal | external [ipv6-prefix ] [link-state-id] | grace | inter-area prefix [ipv6-prefix | link-state-id ...

IS-IS was the first comprehensive link state protocol, and OSPF and NLSP evolved from it. Link state protocols use characteristics of the route such as speed and cost as well as current congestion ...

It’s the Router ID selected by OSPF when the protocol was enabled. This can be chosen automatically or you can manually set this value. Next let’s look at our Link-State Database on R6.