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Chapter 3
Internet Protocols
Synch Sequence
Window: 8192
Checksum: 0x57E7
Urgent Pointer: 0
TCP Options:
Option Type: 2 Maximum Segment Size
Length: 4
MSS: 536
Option Type: 1 No Operation
Option Type: 1 No Operation
Option Type: 4
Length: 2
Opt Value:
No More HTTP Data
Frame Check Sequence: 0x43697363
And sure enough, the source port is over 1024, but the destination port is
80, or HTTP service. The server, or receiving host, will change the destina-
tion port if it needs to.
In the preceding trace, a "syn" packet is sent to the destination device. The
syn sequence is what's telling the remote destination device that it wants to
create a session.
TCP Session: Syn Packet Acknowledgment
The next trace shows an acknowledgment to the syn packet. Notice the "Ack
is valid," which means the source port was accepted and the device agreed to
create a virtual circuit with the originating host:
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
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