Multiplexing conversation using port numbers.ĭata flowing from one application to another is known as a conversation.Ī host can have multiple applications communicating with each other, either within a local network or a remote network.

Ordered data transfer and data segmentation.

These protocols provide different functionalities for different application requirements.Ī few of the most important functionalities are: The transport layer is responsible for the logical communication between applications running on different hosts, thus providing services to application layer protocols on a higher layer of the TCP/IP network model.Įven though many transport layer protocols exist, the two most commonly used protocols are the Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP). It contains a comprehensive set of documents that describes everything required for a computer network to function. The transport layer is part of the TCP/IP networking model, sometimes called the networking architecture. By reading this article, you will understand the workings of TCP and UDP, how they differ from each other, and will also see various applications using these protocols.Īs a prerequisite, a foundational knowledge of TCP/IP Layer 1 and 2 would help any readers understand the article better. Your firewall is working like it should.In this article, we will talk about how applications deliver data between two devices using either Transmission Control Protocol (TCP) or User Datagram Protocol (UDP). I guess that if a TCP FIN or TCP XMAS packet is dropped by the Norton firewall, this is just how it reports it.Įither way, it could be the signs that someone is port scanning you.ĭon't worry about it.

The whole point of this is that there are a lot of TCP packet types. If you get the response that Windows sends out when it sees these packets, you know it is a Windows box, and you can set your attack strategy accordingly. So, a person scanning for Windows systems can use a tool (like NMAP) and send out TCP FIN packets. Therefore, Windows machines cannot process FIN, XMAS or NULL packets. You see, the Windows OS line (from Win95 up to XP) do not follow the RFC guidelines for how TCP/IP communications should be handled. These packet types are useful in determining if a remote system is a Windows machine or not. There are FIN packets, XMAS packets, NULL packets. Now, there are OTHER types of packets that can be sent. Normally, the 3-way TCP handshake is performed by:Ģ: Target is alive and sends SYN/ACK packetģ: Sender acknowledges that target responded and sends an ACK packet. Well, there are other types of TCP packet types other than SYN and ACK.

Tcp packet types