GATE 2006
For which one of the following reasons does Internet Protocol (IP) use the time-
to-live (TTL) field in the IP datagram header?
(A) Ensure packets reach destination within that time
(B) Discard packets that reach later than that time
(C) Prevent packets from looping indefinitely
(D) Limit the time for which a packet gets queued in intermediate routers.

  • Explanation

    Ans : C 

    All options are quite close but C is most appropriate answer.

    Option A says  Ensure packets reach destination within that time, if u think cleverly, TTL field does not ensure delivery of packet at all,time constraint is secondary. So not correct.

    Option B says Discard packets that reach later than that time, but that is not such rule or protocol. Router will discard packets when TTL field is 0 but no time limit constraint is defined. So wrong.

    Option C says Prevent packets from looping indefinitely, it is correct as TTL field will be eventually be 0 so, it will be discarded. It will not consume resource,bandwidth and causing congetion.

    Option D is not appropriate as you can infer from statement.

    Express your views on it.

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