Ccna routing and Switching Complete Study Guide

TCP Session: Syn Packet Acknowledgment

The next trace shows an acknowledgment to the SYN packet:

TCP - Transport Control Protocol

 Source Port:      80 

World Wide Web HTTP

 Destination Port: 1144

 Sequence Number:  2873580788

 Ack Number:       9356571

 Offset:           6

 Reserved:         %000000

 Code:             %010010

      

Ack is valid

      

Synch Sequence

 Window:           8576

 Checksum:         0x5F85

 Urgent Pointer:   0

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TCP/IP and the DoD Model 

107

 TCP Options:

  Option Type: 2 

Maximum Segment Size

    Length:    4

    MSS:       1460

  No More HTTP Data

Frame Check Sequence: 0x6E203132

Notice the 

Ack is valid

, which means that the source port was accepted and the device 

agreed to create a virtual circuit with the originating host.

And here again, you can see that the response from the server shows that the source is 

80 and the destination is the 1144 sent from the originating host—all’s well!

Table 3.2 gives you a list of the typical applications used in the TCP/IP suite by showing 

their well-known port numbers and the Transport layer protocols used by each application 

or process. It’s really key to memorize this table.

Ta b l e   3 . 2     Key protocols that use TCP and UDP