350-001 · Question #1
In order to maintain security, with which hop count are IPv6 neighbor discovery packets sent?
The correct answer is C. 255. IPv6 Neighbor Discovery Protocol (NDP) packets are always sent with a hop limit of 255. This is a critical security mechanism: because every router that forwards a packet decrements the hop limit by 1, any NDP packet that arrives with a hop limit less than 255 must have been…
Question
In order to maintain security, with which hop count are IPv6 neighbor discovery packets sent?
Options
- A0
- B1
- C255
- D256
How the community answered
(23 responses)- A4% (1)
- C91% (21)
- D4% (1)
Explanation
IPv6 Neighbor Discovery Protocol (NDP) packets are always sent with a hop limit of 255. This is a critical security mechanism: because every router that forwards a packet decrements the hop limit by 1, any NDP packet that arrives with a hop limit less than 255 must have been forwarded by at least one router and therefore did not originate from a directly attached neighbor. Receiving devices can reject such packets, preventing off-link attackers from spoofing NDP messages (like Router Advertisements or Neighbor Solicitations). This is defined in RFC 4861 and is the NDP equivalent of a TTL=1 check.
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