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DNS packets


Câu hỏi 1: A closer look at DNS over TCP

Although DNS is mainly used over UDP, there are some situations where it can be used over TCP as well. The attached packet trace contains a TCP connection that was used by dig to interact with the Domain Name System.

Download the packet trace and select the affirmations below that are valid.

If you do not have any packet dissector on your machine, you can visualize the packet trace in the question below.

Câu hỏi 2: The packet trace
# Length Summary Status
0 20 bytes Transmission Control Protocol, Src Port: 39793, Dst Port: 53, Seq: 0, Len: 0
1 20 bytes Transmission Control Protocol, Src Port: 53, Dst Port: 39793, Seq: 0, Ack: 1, Len: 0
2 20 bytes Transmission Control Protocol, Src Port: 39793, Dst Port: 53, Seq: 1, Ack: 1, Len: 0
3 80 bytes Domain Name System (query)
4 20 bytes Transmission Control Protocol, Src Port: 53, Dst Port: 39793, Seq: 1, Ack: 49, Len: 0
5 164 bytes Domain Name System (response)
6 20 bytes Transmission Control Protocol, Src Port: 39793, Dst Port: 53, Seq: 49, Ack: 133, Len: 0
7 20 bytes Transmission Control Protocol, Src Port: 39793, Dst Port: 53, Seq: 49, Ack: 133, Len: 0
8 20 bytes Transmission Control Protocol, Src Port: 53, Dst Port: 39793, Seq: 133, Ack: 50, Len: 0
9 20 bytes Transmission Control Protocol, Src Port: 39793, Dst Port: 53, Seq: 50, Ack: 134, Len: 0

0000  9b7100356120043e  00000000a0005f50  
0010  13030000                            

0000  .q.5a .>......_P
0010  ....            
  • Transmission Control Protocol, Src Port: 39793, Dst Port: 53, Seq: 0, Len: 0
    • Source Port: 39793
      • Destination Port: 53
        • TCP Segment Len: 0
          • Sequence number: 0 (relative sequence number)
            • Acknowledgment number: 0
              • 1010 .... = Header Length: 40 bytes (10)
                • Window size value: 24400
                  • Calculated window size: 24400
                    • Checksum: 0x1303 [unverified]
                      • Urgent pointer: 0
                      0000  00359b715317abd2  6120043fa000ffff  
                      0010  a1c80000                            

                      0000  .5.qS.«Òa .?..ÿÿ
                      0010  ¡È..            
                      • Transmission Control Protocol, Src Port: 53, Dst Port: 39793, Seq: 0, Ack: 1, Len: 0
                        • Source Port: 53
                          • Destination Port: 39793
                            • TCP Segment Len: 0
                              • Sequence number: 0 (relative sequence number)
                                • Acknowledgment number: 1 (relative ack number)
                                  • 1010 .... = Header Length: 40 bytes (10)
                                    • Window size value: 65535
                                      • Calculated window size: 65535
                                        • Checksum: 0xa1c8 [unverified]
                                          • Urgent pointer: 0
                                          0000  9b7100356120043f  5317abd3800000bf  
                                          0010  ced40000                            

                                          0000  .q.5a .?S.«Ó...¿
                                          0010  ÎÔ..            
                                          • Transmission Control Protocol, Src Port: 39793, Dst Port: 53, Seq: 1, Ack: 1, Len: 0
                                            • Source Port: 39793
                                              • Destination Port: 53
                                                • TCP Segment Len: 0
                                                  • Sequence number: 1 (relative sequence number)
                                                    • Acknowledgment number: 1 (relative ack number)
                                                      • 1000 .... = Header Length: 32 bytes (8)
                                                        • Window size value: 191
                                                          • Calculated window size: 24448
                                                            • Window size scaling factor: 128
                                                              • Checksum: 0xced4 [unverified]
                                                                • Urgent pointer: 0
                                                                0000  9b7100356120043f  5317abd3800000bf  
                                                                0010  c0ba000000000000  0000000000000000  
                                                                0020  002ea9be01200001  0000000000000377  
                                                                0030  777713636f6d7075  7465722d6e657477  
                                                                0040  6f726b696e670469  6e666f00001c0001  

                                                                0000  .q.5a .?S.«Ó...¿
                                                                0010  Àº..............
                                                                0020  ..©¾. .........w
                                                                0030  ww.computer-netw
                                                                0040  orking.info.....
                                                                • Transmission Control Protocol, Src Port: 39793, Dst Port: 53, Seq: 1, Ack: 1, Len: 48
                                                                  • Source Port: 39793
                                                                    • Destination Port: 53
                                                                      • TCP Segment Len: 48
                                                                        • Sequence number: 1 (relative sequence number)
                                                                          • Acknowledgment number: 1 (relative ack number)
                                                                            • 1000 .... = Header Length: 32 bytes (8)
                                                                              • Window size value: 191
                                                                                • Calculated window size: 24448
                                                                                  • Window size scaling factor: 128
                                                                                    • Checksum: 0xc0ba [unverified]
                                                                                      • Urgent pointer: 0
                                                                                        • TCP payload (48 bytes)
                                                                                          • PDU Size: 48
                                                                                          • Domain Name System (query)
                                                                                            • Length: 46
                                                                                              • Transaction ID: 0xa9be
                                                                                                • 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.computer-networking.info: type AAAA, class IN
                                                                                                                          • Name: www.computer-networking.info
                                                                                                                            • Name Length: 28
                                                                                                                              • Label Count: 3
                                                                                                                                • Type: AAAA (IPv6 Address) (28)
                                                                                                                                  • Class: IN (0x0001)
                                                                                                                              0000  00359b715317abd3  6120046f80000100  
                                                                                                                              0010  ce510000                            

                                                                                                                              0000  .5.qS.«Óa .o....
                                                                                                                              0010  ÎQ..            
                                                                                                                              • Transmission Control Protocol, Src Port: 53, Dst Port: 39793, Seq: 1, Ack: 49, Len: 0
                                                                                                                                • Source Port: 53
                                                                                                                                  • Destination Port: 39793
                                                                                                                                    • TCP Segment Len: 0
                                                                                                                                      • Sequence number: 1 (relative sequence number)
                                                                                                                                        • Acknowledgment number: 49 (relative ack number)
                                                                                                                                          • 1000 .... = Header Length: 32 bytes (8)
                                                                                                                                            • Window size value: 256
                                                                                                                                              • Calculated window size: 65536
                                                                                                                                                • Window size scaling factor: 256
                                                                                                                                                  • Checksum: 0xce51 [unverified]
                                                                                                                                                    • Urgent pointer: 0
                                                                                                                                                    0000  00359b715317abd3  6120046f80000100  
                                                                                                                                                    0010  58bd000000000000  0000000000000000  
                                                                                                                                                    0020  0082a9be81800001  0003000000000377  
                                                                                                                                                    0030  777713636f6d7075  7465722d6e657477  
                                                                                                                                                    0040  6f726b696e670469  6e666f00001c0001  
                                                                                                                                                    0050  c00c000500010000  0e0f001908636e70  
                                                                                                                                                    0060  33626f6f6b04696e  666f0375636c0261  
                                                                                                                                                    0070  6302626500c03a00  05000100001c1f00  
                                                                                                                                                    0080  0704636e7033c043  c05f001c00010000  
                                                                                                                                                    0090  1c1f0010200106a8  308f0008000082ff  
                                                                                                                                                    00A0  fe68e48c                            

                                                                                                                                                    0000  .5.qS.«Óa .o....
                                                                                                                                                    0010  X½..............
                                                                                                                                                    0020  ..©¾...........w
                                                                                                                                                    0030  ww.computer-netw
                                                                                                                                                    0040  orking.info.....
                                                                                                                                                    0050  À............cnp
                                                                                                                                                    0060  3book.info.ucl.a
                                                                                                                                                    0070  c.be.À:.........
                                                                                                                                                    0080  ..cnp3ÀCÀ_......
                                                                                                                                                    0090  .... ..¨0......ÿ
                                                                                                                                                    00A0  þhä.            
                                                                                                                                                    • Transmission Control Protocol, Src Port: 53, Dst Port: 39793, Seq: 1, Ack: 49, Len: 132
                                                                                                                                                      • Source Port: 53
                                                                                                                                                        • Destination Port: 39793
                                                                                                                                                          • TCP Segment Len: 132
                                                                                                                                                            • Sequence number: 1 (relative sequence number)
                                                                                                                                                              • Acknowledgment number: 49 (relative ack number)
                                                                                                                                                                • 1000 .... = Header Length: 32 bytes (8)
                                                                                                                                                                  • Window size value: 256
                                                                                                                                                                    • Calculated window size: 65536
                                                                                                                                                                      • Window size scaling factor: 256
                                                                                                                                                                        • Checksum: 0x58bd [unverified]
                                                                                                                                                                          • Urgent pointer: 0
                                                                                                                                                                            • TCP payload (132 bytes)
                                                                                                                                                                              • PDU Size: 132
                                                                                                                                                                              • Domain Name System (response)
                                                                                                                                                                                • Length: 130
                                                                                                                                                                                  • Transaction ID: 0xa9be
                                                                                                                                                                                    • Flags: 0x8180 Standard query response, No error
                                                                                                                                                                                      • 1... .... .... .... = Response: Message is a response
                                                                                                                                                                                        • .000 0... .... .... = Opcode: Standard query (0)
                                                                                                                                                                                          • .... .0.. .... .... = Authoritative: Server is not an authority for domain
                                                                                                                                                                                            • .... ..0. .... .... = Truncated: Message is not truncated
                                                                                                                                                                                              • .... ...1 .... .... = Recursion desired: Do query recursively
                                                                                                                                                                                                • .... .... 1... .... = Recursion available: Server can do recursive queries
                                                                                                                                                                                                  • .... .... .0.. .... = Z: reserved (0)
                                                                                                                                                                                                    • .... .... ..0. .... = Answer authenticated: Answer/authority portion was not authenticated by the server
                                                                                                                                                                                                      • .... .... ...0 .... = Non-authenticated data: Unacceptable
                                                                                                                                                                                                        • .... .... .... 0000 = Reply code: No error (0)
                                                                                                                                                                                                        • Questions: 1
                                                                                                                                                                                                          • Answer RRs: 3
                                                                                                                                                                                                            • Authority RRs: 0
                                                                                                                                                                                                              • Additional RRs: 0
                                                                                                                                                                                                                • Queries
                                                                                                                                                                                                                  • www.computer-networking.info: type AAAA, class IN
                                                                                                                                                                                                                    • Name: www.computer-networking.info
                                                                                                                                                                                                                      • Name Length: 28
                                                                                                                                                                                                                        • Label Count: 3
                                                                                                                                                                                                                          • Type: AAAA (IPv6 Address) (28)
                                                                                                                                                                                                                            • Class: IN (0x0001)
                                                                                                                                                                                                                          • Answers
                                                                                                                                                                                                                            • www.computer-networking.info: type CNAME, class IN, cname cnp3book.info.ucl.ac.be
                                                                                                                                                                                                                              • Name: www.computer-networking.info
                                                                                                                                                                                                                                • Type: CNAME (Canonical NAME for an alias) (5)
                                                                                                                                                                                                                                  • Class: IN (0x0001)
                                                                                                                                                                                                                                    • Time to live: 3599
                                                                                                                                                                                                                                      • Data length: 25
                                                                                                                                                                                                                                        • CNAME: cnp3book.info.ucl.ac.be
                                                                                                                                                                                                                                        • cnp3book.info.ucl.ac.be: type CNAME, class IN, cname cnp3.info.ucl.ac.be
                                                                                                                                                                                                                                          • Name: cnp3book.info.ucl.ac.be
                                                                                                                                                                                                                                            • Type: CNAME (Canonical NAME for an alias) (5)
                                                                                                                                                                                                                                              • Class: IN (0x0001)
                                                                                                                                                                                                                                                • Time to live: 7199
                                                                                                                                                                                                                                                  • Data length: 7
                                                                                                                                                                                                                                                    • CNAME: cnp3.info.ucl.ac.be
                                                                                                                                                                                                                                                    • cnp3.info.ucl.ac.be: type AAAA, class IN, addr 2001:6a8:308f:8:0:82ff:fe68:e48c
                                                                                                                                                                                                                                                      • Name: cnp3.info.ucl.ac.be
                                                                                                                                                                                                                                                        • Type: AAAA (IPv6 Address) (28)
                                                                                                                                                                                                                                                          • Class: IN (0x0001)
                                                                                                                                                                                                                                                            • Time to live: 7199
                                                                                                                                                                                                                                                              • Data length: 16
                                                                                                                                                                                                                                                                • AAAA Address: 2001:6a8:308f:8:0:82ff:fe68:e48c
                                                                                                                                                                                                                                                            0000  9b7100356120046f  5317ac57800000c7  
                                                                                                                                                                                                                                                            0010  cd3e0000                            

                                                                                                                                                                                                                                                            0000  .q.5a .oS.¬W...Ç
                                                                                                                                                                                                                                                            0010  Í>..            
                                                                                                                                                                                                                                                            • Transmission Control Protocol, Src Port: 39793, Dst Port: 53, Seq: 49, Ack: 133, Len: 0
                                                                                                                                                                                                                                                              • Source Port: 39793
                                                                                                                                                                                                                                                                • Destination Port: 53
                                                                                                                                                                                                                                                                  • TCP Segment Len: 0
                                                                                                                                                                                                                                                                    • Sequence number: 49 (relative sequence number)
                                                                                                                                                                                                                                                                      • Acknowledgment number: 133 (relative ack number)
                                                                                                                                                                                                                                                                        • 1000 .... = Header Length: 32 bytes (8)
                                                                                                                                                                                                                                                                          • Window size value: 199
                                                                                                                                                                                                                                                                            • Calculated window size: 25472
                                                                                                                                                                                                                                                                              • Window size scaling factor: 128
                                                                                                                                                                                                                                                                                • Checksum: 0xcd3e [unverified]
                                                                                                                                                                                                                                                                                  • Urgent pointer: 0
                                                                                                                                                                                                                                                                                  0000  9b7100356120046f  5317ac57800000c7  
                                                                                                                                                                                                                                                                                  0010  cd3c0000                            

                                                                                                                                                                                                                                                                                  0000  .q.5a .oS.¬W...Ç
                                                                                                                                                                                                                                                                                  0010  Í<..            
                                                                                                                                                                                                                                                                                  • Transmission Control Protocol, Src Port: 39793, Dst Port: 53, Seq: 49, Ack: 133, Len: 0
                                                                                                                                                                                                                                                                                    • Source Port: 39793
                                                                                                                                                                                                                                                                                      • Destination Port: 53
                                                                                                                                                                                                                                                                                        • TCP Segment Len: 0
                                                                                                                                                                                                                                                                                          • Sequence number: 49 (relative sequence number)
                                                                                                                                                                                                                                                                                            • Acknowledgment number: 133 (relative ack number)
                                                                                                                                                                                                                                                                                              • 1000 .... = Header Length: 32 bytes (8)
                                                                                                                                                                                                                                                                                                • Window size value: 199
                                                                                                                                                                                                                                                                                                  • Calculated window size: 25472
                                                                                                                                                                                                                                                                                                    • Window size scaling factor: 128
                                                                                                                                                                                                                                                                                                      • Checksum: 0xcd3c [unverified]
                                                                                                                                                                                                                                                                                                        • Urgent pointer: 0
                                                                                                                                                                                                                                                                                                        0000  00359b715317ac57  6120047080000100  
                                                                                                                                                                                                                                                                                                        0010  cceb0000                            

                                                                                                                                                                                                                                                                                                        0000  .5.qS.¬Wa .p....
                                                                                                                                                                                                                                                                                                        0010  Ìë..            
                                                                                                                                                                                                                                                                                                        • Transmission Control Protocol, Src Port: 53, Dst Port: 39793, Seq: 133, Ack: 50, Len: 0
                                                                                                                                                                                                                                                                                                          • Source Port: 53
                                                                                                                                                                                                                                                                                                            • Destination Port: 39793
                                                                                                                                                                                                                                                                                                              • TCP Segment Len: 0
                                                                                                                                                                                                                                                                                                                • Sequence number: 133 (relative sequence number)
                                                                                                                                                                                                                                                                                                                  • Acknowledgment number: 50 (relative ack number)
                                                                                                                                                                                                                                                                                                                    • 1000 .... = Header Length: 32 bytes (8)
                                                                                                                                                                                                                                                                                                                      • Window size value: 256
                                                                                                                                                                                                                                                                                                                        • Calculated window size: 65536
                                                                                                                                                                                                                                                                                                                          • Window size scaling factor: 256
                                                                                                                                                                                                                                                                                                                            • Checksum: 0xcceb [unverified]
                                                                                                                                                                                                                                                                                                                              • Urgent pointer: 0
                                                                                                                                                                                                                                                                                                                              0000  9b71003561200470  5317ac58800000c7  
                                                                                                                                                                                                                                                                                                                              0010  cd0e0000                            

                                                                                                                                                                                                                                                                                                                              0000  .q.5a .pS.¬X...Ç
                                                                                                                                                                                                                                                                                                                              0010  Í...            
                                                                                                                                                                                                                                                                                                                              • Transmission Control Protocol, Src Port: 39793, Dst Port: 53, Seq: 50, Ack: 134, Len: 0
                                                                                                                                                                                                                                                                                                                                • Source Port: 39793
                                                                                                                                                                                                                                                                                                                                  • Destination Port: 53
                                                                                                                                                                                                                                                                                                                                    • TCP Segment Len: 0
                                                                                                                                                                                                                                                                                                                                      • Sequence number: 50 (relative sequence number)
                                                                                                                                                                                                                                                                                                                                        • Acknowledgment number: 134 (relative ack number)
                                                                                                                                                                                                                                                                                                                                          • 1000 .... = Header Length: 32 bytes (8)
                                                                                                                                                                                                                                                                                                                                            • Window size value: 199
                                                                                                                                                                                                                                                                                                                                              • Calculated window size: 25472
                                                                                                                                                                                                                                                                                                                                                • Window size scaling factor: 128
                                                                                                                                                                                                                                                                                                                                                  • Checksum: 0xcd0e [unverified]
                                                                                                                                                                                                                                                                                                                                                    • Urgent pointer: 0