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6 votes

A IP packet has arrived in which the fragmentation offset value is 100,the value of HLEN is 5 and the value of total length field is 200. What is the number of the last byte?

  1. 194
  2. 394
  3. 979
  4. 1179
in Computer Networks 5.4k views

4 Answers

14 votes
Best answer
Data length=200-4*5=180

Starting number of first byte of fragment=100*8=800

Number of last byte=800+179=979

Ans c

selected by
why 179 is added could you please explain it?
coz there are 180 bytes so + 0-179  @abhishek
@ danny thanx dude..I got it
4*5 means
Someone please answer this
hlen is of 4 bits and it can represent a maximum value of 15. while the header length can g upto 60. so we use a scale factor of 4. so now 4 bits can represent upto 15*4 = 60. so if the value of hlen is 5 then it means it is actually representing 5*4 = 20. hope that clears!
why 100 is multiply by 8. Does it convert into bits?

@ pankajbelwal , scaling factor of fragment offset is 8.


@ayush palak @Raju Kalagoni    But shouldn't data be a multiple of 8? Here data size is 180, which is not a multiple of 8.


@shraddha priya, data need not be a multiple of 8. it doesn't make sense to have data always in multiple of 8. We should always be in a position to send data across network either in multiple of 8 or not.


@shraddha priya Data should be a multiple of 8 in cases where there are more than 1 fragmented packets and all the packets except the last packet must be a multiple of 8. If there is only one packet or the packet is last fragmented packet then it need not be a multiple of 8. 

4 votes

Total Length=200

Data feild excluding header=200-20=180(0---179)

No of byte ahead from this packet is=100*8=800

so last byte =800+179=979
3 votes


An IP packet looks like this.

Header Length = $5*4=20$

So, Payload = $200-20=180$


Fragmentation offset = $100*8=800$

The last byte would be $180 + 800$th = $980th$ but since we number everything from 0 in computer science, it'll be $979th$

0 votes
answer is C

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