Option A (Correct):
In IS-IS, the Designated Intermediate System (DIS) is elected based on the highest configured priority (as defined in Junos OS).
If priorities are equal, the router with the highest MAC address becomes the DIS.
A priority value of 10 will always override a lower priority (e.g., 1).
[Reference: Juniper IS-IS DIS Election., Option C (Correct):, On a multi-access network (e.g., Ethernet), all IS-IS routers form adjacencies with every other router on the segment., Unlike OSPF, IS-IS does not restrict adjacencies to only the DIS., The DIS is responsible for creating a pseudonode LSP to represent the broadcast network, but full mesh adjacencies are maintained., Reference: Juniper IS-IS Adjacency Formation., , , Why Other Options Are Incorrect:, Option B: Incorrect. Higher priority always wins the DIS election. A priority of 1 cannot override a priority of 10., Option D: Incorrect. IS-IS routers form adjacencies with all neighbors, not just the DIS., , , Key Takeaways:, DIS Election: Prioritizes highest numerical value (e.g., 10 > 1)., Adjacency Behavior: Full mesh adjacencies are maintained, unlike OSPF., DIS Role: Primarily for generating pseudonode LSPs and optimizing flooding, not adjacency restriction., For further details, refer to Juniper’s official IS-IS documentation:Juniper IS-IS Configuration Guide., , https://www.juniper.net/documentation/us/en/software/junos/is-is/topics/concept/routing-protocol-is-is-security-designated-router-understanding.html, ]
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