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TOPIC: Fragment Offset Calculation

Fragment Offset Calculation 12 years 2 months ago #5017

  • FallenZer0
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Can anyone be able to calculate what the Fragment Offset would be for the second fragment in the below example?

Lets assume MTU = 1500
Lets say a 2366 byte packet enters an Ethernet network.

Packet 1:

TCP Header = 24Bytes;
IP Header = 20Bytes w/o Options;
Data = 1456Bytes; Flags = 001;

The Fragment Offset will be Zero, since this is the first fragment.

Packet 2:

TCP Header = 24Bytes;
IP Header = 20Bytes w/o options;
Data = 910Bytes; Flags = 010;

Now, what would be the Fragment Offset value for the second fragment?

Sorry Guys, Figured the answer. If anyone is interested, this is how Fragment Offset is calculated.

Fragment offset is measured in the units of 8 Octets.

So, 182 Octets are needed for Data for the first fragment. This is the Start point for the second fragment. So Fragment offset for the second packet is 182.
-There Is A Foolish Corner In The Brain Of The Wisest Man- Aristotle
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Re: Fragment Offset Calculation 11 years 11 months ago #6471

  • tsunami
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:o

I am not quite clear about your posting!
u have not mentioned where(@which layer) the fragmentation is done.
i feel that when a TCP segment is formatted by the IP, there is actually no need for the TCP header to be sent in each fragment.
only the header is sent in the first fragment and in the subsequent fragments only the IP header are sent.

Please calrify.
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