Layer 3 adds logical forwarding details (source and destination IP addresses) so that networking devices can determine the best path toward a destination. This allows an operating system to forward data to an appropriate application or subroutine. For example, TCP port 80 is typically web traffic. This information is encapsulated in TCP and/or UDP with specific port numbers. Take a look at Figure 2-1 to understand how this works.įigure 2-1 OSI Model and Data Encapsulationĭata from the application, presentation, and session layers (Layers 1, 2, and 3) is encapsulated at Layer 4 with transport protocol information. At each layer of the OSI reference model, the data is processed, encapsulated, and sent to the next layer. This information is added in the form of headers and footers. Think of it like an onion, with many layers.
Encapsulation is the method by which information is added at each layer of the OSI reference model, used for processing and forwarding purposes. Encapsulation is an important component of the OSI model for data communication and is absolutely essential in IP networks. Layered Encapsulationīefore reviewing multicast in Layer 2, we must discuss fundamental packet-forwarding concepts to establish a baseline of the process. This chapter covers the basic elements of multicast functionality in Layer 2 domains as well as design considerations for multicast deployments. This chapter takes an in-depth look at IP multicast messages at Layer 2 and how they are transported in a Layer 2 domain. Chapter 1, “Introduction to IP Multicast,” examined the differences between unicast, broadcast, and multicast messages.
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