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A host is sending 100 datagrams to another host. If the identification number of the
first datagram is 1024, what is the identification number of the last (in IPv4)?

my doubt in IPV4,  identification number is same for all the datagram that is 1024 .

but see

The identification field is incremented for each non-fragmented datagram. If the
first is 1024, then the last is 1024 + 99 = 1123

pls clear this
asked in Computer Networks by Loyal (3.5k points)   | 28 views

1 Answer

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Identification number is used to uniquely identify the datagram when it leaves the source host.

For this uniqueness Ipv4 protocol uses a counter to label the datagram. Intiallly the counter is set to any positive number.

When Ipv4 protocol starts sending datagrams it copies the current value of identification field and increments the counter by 1.

When fragmentation is done, the value of fragmentation field is copied to all the fragments i.e all fragments have same identification number as original datagram.

So if source is sending 100 datagrams and for the first datagram identification no is 1024 then for the last datagram identification no is 1024 + 99 = 1123.

Suppose if any of the datagram is fragmented, say 50th datagram is fragmented into 4 fragments then these fragments have same identification no of 1024+49 = 1073.

Hope it clears you. :)
answered by Loyal (3.4k points)  
got it for fragmentation it would be unique not for individual datagram

thnks a lot
Yeah correct

Always welcome :)


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