Find the fragment offset values in the IP header for each fr

Find the fragment offset values in the IP header for each fragment of a datagram with a 400-byte payload (IP header with no options) when the datagram travels through a segment with an MTU = 100 bytes.

Solution

Solution:

The datagram without IP header size= 400-20 = 380 bytes

Now, MTU given is 100. Again subtracting 20 byte from it we get 100 - 20 = 80

the first fragment will be :

380 - 80 = 300 bytes left

Second fragment will be :

300 - 80= 220 bytes

third fragment will be :

220 - 80 = 140 bytes

fourth fragment will be:

140 - 80 = 60 bytes

Fifth fragment will be :

60 bytes along with 20 byte IP header = 80 bytes.

The initial four fragments are also sent with 20 byte IP header along wiht them. Therefore the the total number of byte transmitted increases to 500 (each time a 20 Byte IP header is also included).

Fragment offset value is calculated as a multiple of 8. The fragment offset values are given as follows:

0, 10, 20, 30, 40. //Calculated as the first value will be 80/8 = 10, similarly other three values are // calculated with each segment representing other 80 bytes and for last one it will // be 0.