cisco ccna objectives

cisco ccna objectives.The logical topology of the example is shown in Figure 1.3. As can be seen from the figure, there are two hosts: Host A and Server B, the former requesting to open a web page and the latter being the destination host on which the web resources reside. The two routers R1 and R2 (interconnected by fiber links) are responsible for "connecting" Host A and Server B. Host A and Server B are directly connected to R1 and R2 through physical cables, respectively.Mainframe AFigure 1-3 is used to demonstrate the logical topology of network communication based on the TCP/IP model /hut Figure 1-4 shows the interaction between the layers of the TCP/IP model involved in this example.1.2 TCP/IP and. SI Reference Model 9Figure 1-4 Interaction between the layers of the TCP/IP modelNow, the interaction between the layers of the TCP/IP model is described according to Figure 1.4.Step 1. the HTTP application on Host A creates an HTTP application message that consists of an HTTP header and a netload. the HTTP netload will contain the link to the web page that Host A requested to open. Host A then performs an encapsulation operation at each layer of the TCP/IP protocol stack as shown in Figure 1.2. The encapsulation operation will end at the data link layer, and the Ethernet frame with the encapsulated HTTP message will be delivered to R1 over the physical cable.After receiving the Ethernet frame, R1 will extract the IP packet through the link layer and send it to the IP layer. The primary function of the router is to forward IP packets and does not perform further decapsulation of the packets. R1 will forward the packets to R2, the next-hop router closest to Server B. To do this, R1 will encapsulate the IP packets into new link-layer frames (for example, point-to-point [PPPoA] frames over ATM) before sending them to R2 over the fiber optic link.Step 3. R2 will encapsulate the IP packet into a new Ethernet frame before sending it to Server B, as described for R1 in Step 2.Server B will send the IP packet to the Internet layer by decapsulating the Ethernet frame over the link layer. Step 5.