Made-Easy Test Series

Question

Consider source X and destination Z is connected through an intermediate network Y. X sends a message of 260 bytes of application data to Z. TCP layer at source X prefixes 40 byte header to the message and then IP layer attach 40 byte header. Data link layer attaches a 20 bytes header to the message. This message passes through an intermediate network Y. The maximum packet size including 40 byte IP header at X, Y and Z are 800 bytes, 200 bytes
and 800 bytes respectively?

How many bytes, including headers are delivered to the IP layer at the destination for one message in best case considering only data packets and assuming that packets are correctly delivered. (Consider 40 bytes IP header at each network).

a)400 bytes

b)384 bytes

c)360 bytes

d)424 bytes

Comments

Answer is coming as 420.

MTU is 200 in the router Y.

Data packet size to be sent (excluding IP header) = 300 bytes.

send 160 bytes first. Hence 160 + 40 + 20 (Data link header) reaches the destination first

i.e 220 byes.

Now send the rest 140 bytes

Hence bytes sent = 140 + 40 + 20 = 200 bytes

Thus total bytes sent = 420

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Why are you considering Data Link Layer header size when we are working upon Network Layer. I think that is just a decoy data given in the question.

 I am getting 380 Bytes as answer.