Assume a 1024 byte data packet( packet id : 10 ) has to pass through two network

Question

Assume a 1024 byte data packet( packet id : 10 ) has to pass through two networks whose MTUs are 600 and 400 bytes respectively, to reach the destination. Specify the IP fields related to fragmentation in case of transparent and non-transparent fragmentation
(i) at the source
(ii)while passing through the network whose MTU is 600
(iii)while passing through the network whose MTU is 400
(iv)at the destination
How the destination IP combine these fragments and regenerate the original packet?

( source )--> ( Network N1 , MTU=600 )---> ( Network N2 , MTU = 400)--> ( Destination)

Explanation / Answer

header size not provided taken as 24 bytes. (i)at the source dont fragment bit will be 1 and more fragments bit will be 0 id=10 (ii)when it is passing through a network with MTU=600 then it is divided into 2 fragments and max data in each packet is 600-24=576 so for first fragment MF flag will be 1 and fragment offset =0 and for 2nd fragment MF will be 0 and fragment offset will be 576/8=72 (iii)when it is passign through MTU of 400 bytes max data size will be 400-24=376 so it is divided into 3 fragments. for 1st fragment MF=1 and offset=0 for 2nd fragment MF=1 and offset=376/8=47 for 3rd fragment MF=0 and offset=376*2/8=94 the difference between transparent and non transparent is in transparent fragmentation when it is leaving the network to another network fragments are combined and passed. i think i solved your problem. and MF will be 1 when there are more fragments after that and offset is the offset of data in that fragment in number of "8 bytes"

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