ccna 200-301 network simulator tools today cnc

ccna 200-301 network simulator tools today cnc.k26Chapter 2 Network Interconnection and Reference Models. ** | 02The "Sniffer Software Installation" file. Figure 2-4-1 shows the DNS query and answer packets captured by the Sniffer software.In Figure 241, you can see that a complete TCP/IP application packet is divided into four layers: the Network Access layer, or the "DLC" layer in Figure 2-4.1, which includes the physical layer of the OSI model and the data link layer, where you can see the source and destination MAC addresses of the data frames; the InterNetworking layer, which includes the physical layer and the data link layer of the OSI model; and the InterNetworking layer, which includes the source and destination MAC addresses of the data frames. The Internet layer, or the "IP" layer in Figure 2-4-1, is equivalent to the network layer of the OSI model, where the source and destination IP addresses of packets are visible. The "UDP" layer, consistent with the transport layer in the OSI model, in this layer you can see the data segmentation source and destination ports, as well as the protocol used, from the figure can be seen, DNS services mainly use the UDP protocol, the service port is 53; Application layer (Application), that is, Figure 2-4-1, the "DNS" layer. The "DNS" layer in Figure 2-4-1 includes the upper three layers of the OSI model, i.e., the session layer, the representation layer, and the application layer, where it can be seen that the DNS packet queries the IP address corresponding to the domain name "www.Wu.edu.cn".Figure 2-4-1 TCP/IP four-layer model The ISO/OSI reference model was designed before its protocols were developed. This means that the ISO/OSI model was not designed based on a specific set of protocols, and therefore it is more general in nature. But on the other hand, it also means that the ISO/OSI model has some shortcomings in terms of protocol implementation. The TCP/IP model is the opposite. There are protocols first and the model is just a description of existing protocols, thus the protocols fit the model very well. The problem is that the TCP/IP model does not fit other protocol stacks. Therefore, it is not very useful in describing other non-TCP/IP networks. Here's a look at the specific differences between the two models. One obvious difference is that the two models have different layers: the ISO/OSI model has seven layers, while the TCP/IP model has only four. Both have a transport layer and an application layer, but the other layers are different. The correspondence between the two models is shown in Figure 2-4.2.ISO/OSI TCP/IPApplication Layer Representation House Session Layer 7 Application 6 Presentation 5 Session Application Application LayerTransport Layer 4 Transport Transport Winning LayerNet Silk Layer 3 Netwotk Inteniet Data Link Layer Physical Layer 2 Data Link 1 Physical N etwork Access Network Access Interlayer