Basic Learning: three-layer switching concepts and principles

Basic Learning: the concept and principle of layer-3 switching: layer-2 switching + layer-3 forwarding. It solves the network bottleneck caused by low speed and complexity of traditional routers. Www.2cto.com
What is layer-3 switching, also known as multi-layer switching technology or IP address switching technology, is proposed in contrast to the traditional concept of switching. As we all know, the traditional exchange technology operates on the data link layer, the second layer of the OSI network standard model, the layer-3 switching technology implements high-speed packet forwarding in the layer-3 network model. To put it simply, layer-3 switching technology is layer-2 switching technology + layer-3 forwarding technology. The emergence of layer-3 switching technology solves the problem that the subnet must be managed by routers after the network segments are divided in the LAN, and solves the network bottleneck caused by the low speed and complexity of traditional routers. Layer-3 switching principle a device with layer-3 switching function is a layer-2 switch with layer-3 routing function, but it is an organic combination of the two, it is not simply to overlay the hardware and software of a router device on a LAN switch. The principle is: Assume that two sites A and B that use the IP protocol communicate with each other through the layer-3 Switch. When sending Site A, compare its IP address with the IP address of site B, determine whether Site B is in the same subnet as itself. If the destination site B and the destination site A are in the same subnet, Layer 2 Forwarding is performed. If two sites are not in the same subnet, if Station A needs to communicate with Station B, station A must send an ARP (Address Resolution) packet to the "Default Gateway, the IP address of the "Default Gateway" is actually a layer-3 Switch module. Www.2cto.com when station A broadcasted an ARP request to the IP address of the "Default Gateway", if the layer-3 Switching Module knew the MAC address of Station B during the previous communication, then the MAC address of B is returned to the sending Site. Otherwise, the layer-3 Switch module broadcasts an ARP request to Site B based on the route information. Site B receives the ARP request and then replies to the layer-3 Switch module with its MAC address, the layer-3 Switching Module saves the address and sends it back to the sender Site A. It also sends the MAC address of Site B to the MAC address table of the layer-2 switching engine. After that, when A sends all the packets to B, the information can be exchanged at A high speed. Because layer-3 processing is only required in the routing process, most of the data is forwarded through layer-2 switch, so the speed of layer-3 switch is very fast, close to the speed of layer-2 switch, and the price is much lower than that of the same router.