Understanding the LSDB and Level-2 DIS Election in IS-IS:
In IS-IS, theDesignated Intermediate System (DIS)is elected for both Level-1 and Level-2 on broadcast networks to manage the link-state database (LSDB) and reduce the number of LSAs exchanged.
The election of the DIS is based on thehighest priority. If the priority is the same, the router with thehighest System IDbecomes the DIS.
HCIP-Datacom-Core Technology Training Material (IS-IS DIS Election).
Analyzing the LSDB:
From the LSDB ofR1, the Level-2 link-state database includes the following entries:
LSPID 0100.0000.3003.00-00: This is R3, and it is present in the Level-2 LSDB with the sequence number and checksum details.
Other routers (R1, R2, R4) are present but do not have the characteristics of the Level-2 DIS in this topology.
Based on the System IDs,R3 (0100.0000.3003)has the highest System ID, making it theLevel-2 DIS.
Conclusion:
The Level-2 DIS on the network isR3, based on the election rules and the LSDB information shown in the figure.
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