OSPF - Link ID in the OSPF database

Within the construct of the OSPF database in a Cisco router, the Link ID can have various meanings.

The show ip ospf database command will provide output that is similar to this:

R1#show ip ospf database
Link ID         ADV Router      Age         Seq#       Checksum Link count
10.0.13.1       10.0.13.1       1865        0x80000007 0x002244 3

Because this is a Type 1 LSA the content of the Link ID column here refers to the Router ID of the router that generated the LSA.

Now if you issue the command show ip ospf database router 10.0.13.1 it will display detailed information about the Type 1 LSAs generated by that router, and it may look something like this:

R1#show ip ospf database router 10.0.13.1

  Link connected to: a Transit Network
    (Link ID) Designated Router address: 10.0.13.3
    (Link Data) Router Interface address: 10.0.13.1
     Number of MTID metrics: 0
      TOS 0 Metrics: 1

The Link ID shown here under the section labeled Link connected to: a Transit Network, refers to the router ID of the DR that was elected on that particular network segment.

The Link ID in this context represents the Router ID of the DR on that network, which could be different from the Router ID of the router that generated the LSA.

Therefore, the Router ID (Link ID in the first command) and the Designated Router’s ID (Link ID in the second command) are not the same thing, even though they are labeled as the same in the output shown.

https://networklessons.com/ospf/how-to-read-the-ospf-database https://networklessons.com/ospf/ospf-lsa-types-explained/ https://networklessons.com/ospf/ospf-router-id

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