8: TCP Disconnect Request

This is one of a series of 9 packets corresponding to the setup and clear-down of a TCP connection. In this case the connection was made to the telnet (terminal) port of the remote computer. The computer accepts the connection and produces a login prompt to the client. Instead of proceeding to login to the server, the client then decides to terminate the connection.

This packet clears-down the telnet connection from the client to the server. The FIN (Final) bit in the TCP header is set to indicate that the client wishes the end of the connection. Normally the server would reply with another TCP packet also with the FIN bit set, confirming that the connection has been disconnected. In this case, (as shown in 9,10) the remote node decides to continue transmission.


Hexadecimal Dump of the Packet

           0: 00e0 f726 3fe9 0800 2086 354b 0800 4500    ..÷&?... .5K..E.
          16: 0028 08bb 4000 ff06 9998 8b85 d96e 8b85    .(..@........n..
          32: e902 9005 0017 7214 f130 9431 1028 5011    ......r..0.1.(P.
          48: 2238 1c64 0000                             "8.d..


Decode of the Packet

ETHER:  ----- Ether Header -----
ETHER:
ETHER:  Packet 8 arrived at 17:37:31.08
ETHER:  Packet size = 54 bytes
ETHER:  Destination = 0:e0:f7:26:3f:e9,CISCO Router
ETHER:  Source      = 8:0:20:86:35:4b, Sun
ETHER:  Ethertype = 0800 (IP)
ETHER:
IP:   ----- IP Header -----
IP:
IP:   Version = 4
IP:   Header length = 20 bytes
IP:   Type of service = 0x00 (normal)
IP:   Total length = 40 bytes
IP:   Identification = 2235
IP:   Flags = 0x4
IP:         .1.. .... = do not fragment
IP:         ..0. .... = last fragment
IP:   Fragment offset = 0 bytes
IP:   Time to live = 255 seconds/hops
IP:   Protocol = 6 (TCP)
IP:   Header checksum = 9998
IP:   Source address = 139.133.217.110, client
IP:   Destination address = 139.133.233.2, server.abdn.ac.uk
IP:   No options
IP:
TCP:  ----- TCP Header -----
TCP:
TCP:  Source port = 36869
TCP:  Destination port = 23 (TELNET)
TCP:  Sequence number = 1913975088
TCP:  Acknowledgement number = 2486243368
TCP:  Data offset = 20 bytes
TCP:  Flags = 0x11
TCP:        ..0. .... = No urgent pointer
TCP:        ...1 .... = Acknowledgement
TCP:        .... 0... = No push
TCP:        .... .0.. = No reset
TCP:        .... ..0. = No Syn
TCP:        .... ...1 = Fin
TCP:  Window = 8760
TCP:  Checksum = 0x1c64
TCP:  Urgent pointer = 0
TCP:  No options
TCP:


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