By default, how many seconds is the retransmission interval of LSP messages on a point-to-point link?

Question

Options

• A5
• B4
• C60
• D10

• A
  6% (2)
• B
  3% (1)
• C
  11% (4)
• D
  81% (29)

Explanation

Option D (10 seconds) is correct because, by default in IS-IS, if a router sends an LSP (Link State PDU) on a point-to-point link and does not receive an acknowledgment, it will retransmit that LSP after a 10-second interval - this is the standard default retransmit timer configured on point-to-point interfaces.

Why the distractors are wrong:

• A (5 seconds) is a common trap; 5 seconds is often associated with IS-IS Hello interval timers, not the LSP retransmit interval.
• B (4 seconds) has no standard role in IS-IS timer defaults and is simply incorrect.
• C (60 seconds) is also used in IS-IS, but it refers to the LSP minimum interval (how often a new LSP can be originated), not the retransmit interval.

Memory tip: Think "10 seconds to re-transmit, 5 seconds to say hello." The retransmit interval (10s) is double the Hello interval (5s), which makes intuitive sense - you give the neighbor a beat longer to acknowledge a full LSP than a simple keepalive.

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