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ccna 200 301 syllabus plural spelling of attorneys.Interconnecting a network with other networks, getting more information from the network and distributing oneself to the network is the most important motivation for network interconnection. There are several ways to interconnect networks, the most used of which are switch interconnection and router interconnection.1. Switch interconnection network switches work at layer 2 of the OSI model, the data link layer. It completes the forwarding of data frames (Frames) with the main purpose of providing transparent communication between the connected networks. The switch's forwarding relies on the source and destination addresses in the data frame to determine whether a frame should be forwarded and to which port it should be forwarded. The address in the frame is called the "MAC" address or "hardware" address, and is generally the address of the network card. The role of a switch is to interconnect two or more networks and provide transparent communication. The devices on the network are invisible to the switch, and communication between devices is as easy as if they were on a network. Since switches forward on data frames, they can only connect identical or similar networks (data frames of the same or similar structure), such as interconnections between Ethernet and between Ethernet and token rings, and cannot do anything for different types of networks (different data frame structures), such as interconnections between Ethernet and X.25. Switches expand the size of the network, improve the performance of the network, and bring convenience to network applications, and they were more widely used in previous networks. However, switch interconnection also brings a lot of problems: the first problem is broadcast storms. Switches cannot block broadcast messages in the network, and when the scale of the network is large (several switches, multiple Ethernet segments), it may cause broadcast storms, resulting in the entire network being filled with broadcast messages until it is completely paralyzed. The second problem is network interconnection. The switch is a data link layer device that cannot complete interconnection between different IP segments,The second problem is network interconnection, the switch is a data link layer device, can not complete the interconnection between different IP network segments, fCCNA Study and Lab Guide that is, no matter how many interconnected devices, these devices can only be in the same IP subnet, if a department and another department in a different IP subnet, the switch will not be able to complete the network interconnection.The third problem is network security, the switch can not achieve the connection of different IP subnets, the solution is to configure both sides of the network devices in the same IP subnet, when interconnected with the external network, the internal and external network into one, into a network, both sides are completely open to each other their network resources, for security reasons, this is not allowed in many networks.2. Router interconnection networkRouter interconnection is related to the protocol of the network, and this book will only discuss the case of TCP/IP networks. Routers work at layer 3 of the OSI model, the network layer. Routers use "logical" addresses (i.e., IP addresses) defined at the network layer to distinguish between networks, interconnect and isolate them, and maintain the independence of each network. Routers do not forward broadcast messages, but rather restrict them to their respective networks. Packets sent to other networks are first sent to the router, which then forwards them out.IP routers only forward IP packets, keeping the rest of the network (including broadcasts) inside, thus maintaining the relative independence of each network and allowing the formation of large networks with many networks (subnets) interconnected. Because of the interconnection at the network layer, routers make it easy to connect different types of networks that can be interconnected through routers as long as the network layer is running the IP protocol.Devices in the network communicate with each other using their network addresses (IP addresses in TCP/IP networks). IP addresses are "logical" addresses that have nothing to do with hardware addresses. Routers forward data based on IP addresses, which are structured in two parts, one defined as the network number and the other defined as the host number within the network. Currently, subnet masks are used in Internet networks to determine the network address and host address in an IP address. The subnet mask is 32 bits, like the IP address, and the two are one-to-one, and the part of the IP address that corresponds to a "1" in the subnet mask is the network number, while the part that corresponds to a "0" is the host number. The network number and the host number together constitute a complete IP address. The IP addresses of hosts in the same network must have the same network number, and this network is called an IP subnet.Hosts with the same network number can communicate directly with each other, but to communicate with hosts on other IP subnets, they must go through a router or gateway on the same network. IP addresses with different network numbers cannot communicate directly, even if they are connected together.A router has multiple ports for connecting to multiple IP subnets, and the network number of the IP address on each port should be the same as the network number of the IP subnet to which it is connected. Different ports correspond to different IP subnets, and the network numbers of multiple ports of the router must be different.