This field identifies the piece of the routing domain that
is being described by the LSA.
What value is populated into this field depends on the type of LSA. This is also described in the same section of that RFC.
The “Link State ID” field is an identifier for the LSA, to make this LSA different from any other LSA from this advertising router. Within the body of the LSA, every actual link (GigEthernet, Serial, Loopback, etc) is also given a unique value called a “Link ID”.
why your answer is become hard ?please don`t do that
please sir when you explain anything to me try to explain it a little easier in order to understand.also providing examples is helpful for better understanding.
ok no problem i understand that
that is the point i`m asking about . in the show ip ospf data output i see this headline
Link ID 0.0.0.1
but in the show ip ospf data router i see this output
Link State ID 0.0.0.1
what is that ?
The Link-State ID field in the LSA header doesn’t really have much of a purpose for Type-1 Router LSAs. This is because for a given area (like Area-0) that a router may be connected to, it will only generate one (1) Type-1 Router LSA for that area and describe all of its links in that area within that single Router LSA. So in my opinion, that single LSA could easily be described by just stamping it with your Advertising Router-ID value as well as the sequence number. The Link-State ID field is just a copy of the Advertising Router ID (in the Type-1 Router LSA).
However, when thinking about Type-3 Summary LSAs and Type-5 AS-External LSAs, the Link-State ID field actually does have a lot of relevance. Those LSAs describe only a single link and the Link-State ID field provides the prefix on that link. So I’m guessing that since it was a required element of the LSA header for those LSA types, the designers of OSPF probably just retained that field for the Type-1 Router LSA. But since the Type-1 Router LSA could describe several links, they just decided to populate it with the Advertising Router-ID.