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Author(s) Olivier Bonaventure
Deadline No deadline
Submission limit No limitation
Category tags IPv6

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IPv6 : packet fragmentation, a simple example

IPv6, described in the IPv6 chapter of Computer Networking: Principles, Protocols and Practice includes a packet fragmentation mechanism that allows to send large packets as a series of fragments.


Reorder the fragments

Can you reorder the packet packet fragments that were captured while a host was using ping6 to verify the reachability of destination 2001:7ab:2::b with packets that are longer than the MTU ? This packet was sent by a Linux host that sends the first fragment of the packet last.

# Length Summary Status
0 40 bytes Internet Protocol Version 6, Src: 2001:7ab:1::a, Dst: 2001:7ab:2::b
1 40 bytes Internet Protocol Version 6, Src: 2001:7ab:1::a, Dst: 2001:7ab:2::b

0000  6000df0404d82c3e  200107ab00010000  
0010  000000000000000a  200107ab00020000  
0020  000000000000000b                    

0000  `.ß..Ø,> ..«....
0010  ........ ..«....
0020  ........        
  • Internet Protocol Version 6, Src: 2001:7ab:1::a, Dst: 2001:7ab:2::b
    • 0110 .... = Version: 6
      • .... 0000 0000 .... .... .... .... .... = Traffic Class: 0x00 (DSCP: CS0, ECN: Not-ECT)
        • .... 0000 00.. .... .... .... .... .... = Differentiated Services Codepoint: Default (0)
          • .... .... ..00 .... .... .... .... .... = Explicit Congestion Notification: Not ECN-Capable Transport (0)
          • .... .... .... 0000 1101 1111 0000 0100 = Flow Label: 0x0df04
            • Payload Length: 1240
              • Next Header: Fragment Header for IPv6 (44)
                • Hop Limit: 62
                  • Source: 2001:7ab:1::a
                    • Destination: 2001:7ab:2::b
                    0000  6000df0402382c3e  200107ab00010000  
                    0010  000000000000000a  200107ab00020000  
                    0020  000000000000000b                    

                    0000  `.ß..8,> ..«....
                    0010  ........ ..«....
                    0020  ........        
                    • Internet Protocol Version 6, Src: 2001:7ab:1::a, Dst: 2001:7ab:2::b
                      • 0110 .... = Version: 6
                        • .... 0000 0000 .... .... .... .... .... = Traffic Class: 0x00 (DSCP: CS0, ECN: Not-ECT)
                          • .... 0000 00.. .... .... .... .... .... = Differentiated Services Codepoint: Default (0)
                            • .... .... ..00 .... .... .... .... .... = Explicit Congestion Notification: Not ECN-Capable Transport (0)
                            • .... .... .... 0000 1101 1111 0000 0100 = Flow Label: 0x0df04
                              • Payload Length: 568
                                • Next Header: Fragment Header for IPv6 (44)
                                  • Hop Limit: 62
                                    • Source: 2001:7ab:1::a
                                      • Destination: 2001:7ab:2::b