TTL behavior: Which statement is true about TTL in IP packets?

• A. TTL is decremented by each router hop
• B. TTL is fixed per packet and never changes
• C. TTL increases with each hop
• D. TTL is only used in UDP

Answer: (A)

TTL is the time-to-live field in the IP header that limits how far a packet can travel. As the packet is forwarded from router to router, each hop decreases the TTL by one. When TTL reaches zero, the packet is dropped and an ICMP Time Exceeded message may be sent back to the sender. This prevents infinite looping due to routing errors. The TTL value is set by the sender when the packet is created and then changes as the packet moves; it is not fixed and does not increase with hops. Also, TTL applies to IP packets regardless of the transport protocol (UDP or TCP).