In IS-IS, DIS is used to create and update pseudo nodes, and is responsible for generating link state protocol data unit LStP of pseudo nodes. What is the priority of DIS by default?

Question

Options

• A10
• B64
• C0
• D127

• A
  5% (2)
• B
  75% (30)
• C
  13% (5)
• D
  8% (3)

Explanation

In IS-IS, the default DIS priority is 64, placing it roughly in the middle of the valid range (0 to 127), which allows network administrators flexibility to raise or lower it relative to the default. Option A (10) is incorrect - no standard IS-IS specification defines 10 as a default; it may be confused with defaults from other protocols. Option C (0) is incorrect because a priority of 0 specifically disqualifies a router from DIS election entirely, making it a special-case value rather than a default. Option D (127) is incorrect because that is the maximum possible priority, used to force DIS election, not the default.

Memory tip: Picture the 0-127 scale as a ruler - 0 means "never elect me," 127 means "always elect me," and 64 sits right near the halfway mark as the neutral factory default.

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