In IPv6, which header field is decremented at each hop and is equivalent to TTL?

• A. Traffic Class
• B. Next Header
• C. Payload Length
• D. Hop Limit

Answer: (D)

Hop Limit is the field in IPv6 that serves the same purpose as TTL in IPv4. It is decremented by one each time a router forwards the packet to the next hop, and when it reaches zero the packet is discarded to prevent looping. This mechanism controls how far a packet can travel and triggers an ICMPv6 Time Exceeded message back to the sender if the packet would otherwise loop or wander too long. The other header fields have different roles: Traffic Class is for quality of service, Next Header indicates the type of the following header, and Payload Length shows the size of the payload.