cisco ccna new exam

cisco ccna new exam.As an example, the TCP/IP stack running on a particular personal computer is implemented to allow network communication. The linklayer provides services to the IP layer (e.g., Ethernet frames to encapsulate IP packets), the IP layer provides services to the transport layer (e.g., IP routing and IP addressing), and so on. These are examples of the lower layers of the TCP/IP stack providing services to the upper layers within the same host.Now suppose the reader wants to use that personal computer to connect to a Web server (for example, the reader wants to browse the Web). The Web server must also implement the TCP/IP stack. At this point, the IP layer of that PC and the IP layer of the Web server will communicate via the same protocol, IP Protocol One. The transport layer of both devices will also communicate with each other using the same protocol (TCP), and so on. These are examples of different hosts communicating with each other at the same protocol layer.The subsequent section of this chapter, "Network Communication Based on the TCP/IP Model," describes in detail how two hosts communicate with each other and how the TCP/IP stack works within the same host.Each layer of the TCP/IP stack is analyzed below./SiHLink layer: serves to support the transmission of data over physical (lines) and contains the protocols used to transfer information over the link between the value points of two devicesof the link and the protocols used to transfer information over it. Simply put, the hardware and protocols involved in the link layer are essential to allow two hosts, interconnected by physical links (e.g., cables) or by air (e.g., radio waves), to transmit information to each other. The link layer also involves the concept and mechanisms for replicating and retransmitting information over multiple ports (or multiple links) by dedicated devices (e.g., switches or bridges).Because of the variety of physical media used to transmit information, there are a variety of protocols that operate at the link layer, the more common being the Ethernet protocol. As mentioned before, today the link layer is generally further divided into a physical layer (involving bit [bit] transfer over the physical medium) and a data link layer (providing functions such as encapsulation, addressing, and abstraction of the upper layers). The unit of a message passed at the link layer is called a frame (sh ame). Internet layer: Because devices are not all directly connected to each other, it is common to encounter situations where information is passed across multiple devices. The Internet layer provides networking services, including protocols that support the transfer of information "across" multiple devices (multi-hop). That is, each host involved in the message transfer is identified by an Internet Protocol (IP) address, or another address if another Internet protocol is used. Each hop device (called a network node) between the two hosts involved in message delivery knows how to deliver the message to the host with the destination IP address and will first deliver the message to the nearest next-stop node leading to the destination host.6 Chapter 1 Network Protocols and Network Device Basics