One of the header fields in an IP datagram is the Time to Live (TTL) field.…
201020252024
One of the header fields in an IP datagram is the Time to Live (TTL) field. Which of the following statements best explains the need for this field?
- A.
It can be used to prioritize packets
- B.
It can be used to reduce delays
- C.
It can be used to optimize throughput
- D.
It can be used to prevent packet looping
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Correct answer: D
Key idea: The TTL field limits how long a packet can remain in the network by being decremented at each hop (measured in hops).
Each router that forwards the packet decreases the TTL by one. If the TTL reaches zero, the router discards the packet.
Discarding packets whose TTL expired prevents packets caught in routing loops from circulating forever.
In IPv4, an ICMP "Time Exceeded" message is typically sent to the sender when a packet is dropped for TTL expiry. IPv6 uses an equivalent field called Hop Limit.
Note: TTL is not for prioritization, delay reduction, or throughput optimization—those are handled by other mechanisms (e.g., DSCP/TOS for priority, routing/queuing for delays, and transport-layer congestion control for throughput).
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