What is true about the Hop Limit field in the IPv6 header?

Question

Options

• AThe field is not changed during the transport of a package.
• BThe field is transmitted within a hop-by-hop extension header.
• CEach router forwarding the packet increases the field's value.
• DEach router forwarding the packet decreases the field's value.
• EFor multicast packages, the field's value is always 1.

• A
  2% (1)
• B
  7% (3)
• C
  12% (5)
• D
  76% (31)
• E
  2% (1)

Explanation

D is correct because the Hop Limit field in the IPv6 header serves the same purpose as the TTL (Time To Live) field in IPv4 - each router that forwards the packet decrements the value by 1, and when it reaches 0, the packet is discarded (preventing infinite routing loops).

Why the distractors are wrong:

• A is wrong because routers actively modify this field on every hop - it changes at each forwarding step.
• B is wrong because the Hop Limit is part of the fixed IPv6 base header (40 bytes), not an extension header; hop-by-hop options are a separate extension header type.
• C is wrong - routers decrease, not increase, the value; incrementing would defeat the loop-prevention purpose entirely.
• E is wrong because multicast uses a Hop Limit of 1 only for link-local scope (e.g., neighbor discovery), not for all multicast traffic, which can use higher values depending on the scope.

Memory tip: Think of the Hop Limit as a "life counter" - every router takes one life away. When lives hit zero, the packet dies. IPv6 renamed TTL to "Hop Limit" to be more honest about what it actually counts: hops, not time.

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