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Suppose that host A is connected to a router R1, R1 is connected to another router R2 and R2 is connected to host B. Suppose that a TCP message that contains 900 bytes of data and 20 bytes of TCP header is passed to the IP layer at host A for delivery to B. Assume that link A-R1 can support a maximum frame size of 1024 bytes including a 14-byte frame header, link R1-R2 can support a maximum frame size of 512 bytes, including an 8-byte frame header, and link R2-B can support a maximum frame size of 512 bytes including a 12-byte frame header. Which of the following is correct about the Total length, DF, MF and Fragment offset fields of the IP header in the last packet transmitted over the link R1-R2?


  1. LENGTH=500; DF=0;MF=0;Offset=63
  1. LENGTH=500; DF=0;MF=1;Offset=60
  1. LENGTH=424; DF=0;MF=0;Offset=63
  1. LENGTH=460; DF=0;MF=0;Offset=60.  


(Given ans is C can anyone help with this question whether ans is D or C? )

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getting D.
Answer must be D.

1 Answer

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From TCP 900+20=920

From IP 920+20=940

A to R1 line // MTS=1010+14=1024  Data need to be=1010       No fragmentation

R1 - R2 line //MTS=504+8 =512  Data need to be =504    920 Fragmented as

0 - 503 --> 504

504 - 919 --> 416  // Length =416+8=424

Offset last frame 504/8 =63

MF=0 // last frame


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