in Computer Networks
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23 votes
23 votes

For which one of the following reasons does internet protocol(IP) use the time-to-live(TTL) field in IP datagram header?

  1. Ensure packets reach destination within that time
  2. Discard packets that reach later than that time
  3. Prevent packets from looping indefinitely
  4. Limit the time for which a packet gets queued in intermediate routers
in Computer Networks
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4 Answers

14 votes
14 votes
Best answer

Answer: C

The standard header that is used in$IPv4$ contains key information about an Internet Protocol (IP) packet. Information includes the source and destination IP addresses of the datagram, fragmentation control parameters, and packet length. Another key element of this header is the TTL field. The TTL field consists of a single byte and is capable of holding a value from $0–255. $

Because IP is connectionless, the TTL field was included in the IP header by the original designers as a mechanism to limit the life span of packets within the network. A routing loop is the most common example used to illustrate why this functionality is required. Without such a control mechanism, a routing loop could cause a packet to circle a network infinitely, depleting bandwidth and eventually destabilizing the network. As insurance against this outcome, the TTL value of an IP datagram is decremented by a value of one each time the packet is forwarded by a network device. Thus, an IP packet can never be forwarded more than $254$ times, preventing the infinite packet loop problem.

https://tools.cisco.com/security/center/resources/ttl_expiry_attack.html

edited by

4 Comments

@Deepak Poonia how 254….?
shouldn't be 255.

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1
ok i got it, forwarding….my bad.
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0

@Deepak Poonia if this question was MSQ, is option b also correct?

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@JAINchiNMay @Abhrajyoti00

can you elaborate a bit about 254…

@Raniya1

option b is not correct, even if question is MSQ.

Packet reaching later is different thing and TTL is different.

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15 votes
15 votes

Answer is (C).

Prevent the packet to involve in infinite loop and also to prevent  server crash. That's why TTL field is used into this in the IPv4 datagram field.

edited by
7 votes
7 votes
Answer is Option C)

IP (Internet Protocol) uses TTL (Time-to-Live) because it indicates how long a packet should be in the network. This field limits the lifespan of data in a computer network. It may be implemented as counter or timestamp, thereby prevents a data packet from looping indefinitely.
0 votes
0 votes

Time-to-live (TTL) is a value in an Internet Protocol (IP) packet that tells a network router whether or not the packet has been in the network too long and should be discarded.

Answer:

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