Multiple choice

Which field of the IP header helps to prevent datagrams from persisting on an internet?

  1. Destination address

  2. Source address

  3. Flag

  4. TTL

  5. Header checksum
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

An eight-bit time to live field helps prevent datagrams from persisting (e.g. going in circles) on an internet. This field limits a datagram's lifetime. It is specified in seconds, but time intervals less than 1 second are rounded up to 1. In practice, the field has become a hop count—when the datagram arrives at a router, the router decrements the TTL field by one. When the TTL field hits zero, the router discards the packet and typically sends an ICMP Time Exceeded message to the sender.

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