TCP Traffic
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TCP Overview
TCP or Transmission Control Protocol handles the delivery of packets including sequencing and errors. You should already have an understanding of how TCP works, if you need a refresher check out the .
Below you can see a sample of a Nmap scan, scanning port 80 and 443. We can tell that the port is closed due to the RST, ACK packet in red.
When analyzing TCP packets, Wireshark can be very helpful and color code the packets in order of danger level. If you can't remember the color code go back to Task 3 and refresh on how Wireshark uses colors to match packets.
TCP can give useful insight into a network when analyzing however it can also be hard to analyze due to the number of packets it sends. This is where you may need to use other tools like RSA NetWitness and NetworkMiner to filter out and further analyze the captures.
TCP Traffic Overview
A common thing that you will see when analyzing TCP packets is known as the TCP handshake, which you should already be familiar with. It includes a series of packets: syn, synack, ack; That allows devices to establish a connection.
Typically when this handshake is out of order or when it includes other packets like an RST packet, something suspicious or wrong is happening in the network. The Nmap scan in the section above is a perfect example of this.
TCP Packet Analysis
For analyzing TCP packets we will not go into the details of each individual detail of the packets; however, look at a few of the behaviors and structures that the packets have.
Below we see packet details for an SYN packet. The main thing that we want to look for when looking at a TCP packet is the sequence number and acknowledgment number.
In this case, we see that the port was not open because the acknowledgment number is 0.
Within Wireshark, we can also see the original sequence number by navigating to edit > preferences > protocols > TCP > relative sequence numbers (uncheck boxes).
Typically TCP packets need to be looked at as a whole to tell a story rather than one by one at the details.
Read the above and move into Task 10.
