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

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DNS and the UDP port numbers


The UDP port numbers

DNS messages are carried inside UDP segments. Could you predict the source and destination port numbers of the DNS response knowing the DNS request ?


0000  f696003500294709  16eb012000010000  
0010  0000000003777777  076578616d706c65  
0020  036f726700001c00  01                

0000  ö..5.)G..ë. ....
0010  .....www.example
0020  .org.....       
  • User Datagram Protocol
    • Source Port: 63126
      • Destination Port: 53
        • Length: 41
          • Checksum: 0x4709 [unverified]
          • Domain Name System (query)
            • Transaction ID: 0x16eb
              • Flags: 0x0120 Standard query
                • 0... .... .... .... = Response: Message is a query
                  • .000 0... .... .... = Opcode: Standard query (0)
                    • .... ..0. .... .... = Truncated: Message is not truncated
                      • .... ...1 .... .... = Recursion desired: Do query recursively
                        • .... .... .0.. .... = Z: reserved (0)
                          • .... .... ..1. .... = AD bit: Set
                            • .... .... ...0 .... = Non-authenticated data: Unacceptable
                            • Questions: 1
                              • Answer RRs: 0
                                • Authority RRs: 0
                                  • Additional RRs: 0
                                    • Queries
                                      • www.example.org: type AAAA, class IN
                                        • Name: www.example.org
                                          • Name Length: 15
                                            • Label Count: 3
                                              • Type: AAAA (IPv6 Address) (28)
                                                • Class: IN (0x0001)