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Author(s) Olivier Bonaventure
Deadline No deadline
Submission limit No limitation
Category tags ipv6

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IPv6 : packet forwarding

IPv6 is described in the IPv6 chapter of Computer Networking: Principles, Protocols and Practice. When a router forwards a packet, it updates some of its fields.

Packet forwarding

The first packet was captured on an ingress interface of a router. The second was captured on its egress interface after having been forwarded. Can you infer the different fields of the forwarded packet ?

# 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  6000df0400403a40  200107ab00010000  
0010  000000000000000a  200107ab00020000  
0020  000000000000000b                    
0000  `.ß..@:@ ..«....
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: 64
              • Next Header: ICMPv6 (58)
                • Hop Limit: 64
                  • Source: 2001:7ab:1::a
                    • Destination: 2001:7ab:2::b
                    0000  6000df04????????  ????????????????  
                    0010  ????????????????  ????????????????  
                    0020  ????????????????                    
                    0000  `.ß.????????????
                    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: ?
                              • Next Header: ICMPv6 (?)
                              • Hop Limit: ?
                              • Source: ?
                              • Destination: ?