[ee122] [EE122] Question on IP Fragmentation

Jonathan D. Ellithorpe jde at berkeley.edu
Thu Oct 11 19:54:39 PDT 2007

On slides 21, 22, and 23 of lecture 4, I noticed something confusing 
about the length field of fragment 1 (slide 21), and the offset of 
fragment 2 (slide 22). Shouldn't the offset of fragment 2 denote the 
location of where data should be concatenated in memory on the receiver? 
If so, I'm not sure why the length of frag 1 is 1496 and the offset of 
frag 2 is 1496. It would seem to me that, if the IP header were 20 
bytes, then the offset of frag 2 should be 1476, because the data of 
frag 1 was 1476 bytes long, (bytes 0 to 1475 in the receiving host's 
memory). Thus, frag 2's offset should be 1476, to denote where frag 2's 
data should start.

Thanks for any help I can get on understanding this!


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