Introduction: The Routing Connections of Layer 3 Ethernet Switch-VSOL

The Layer 3 switch also has a certain "routing" function, which can realize the connection of different subnets. However, it should be noted that its routing function is much weaker than that of a router. The routing function of the third layer switch can only be used for the same type of network interconnection, usually only for the interconnection between LAN subnets. It cannot connect a LAN with a WAN or the Internet because layer 3 switches support very limited routing protocols. After all, that's not its main function.

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We know that on the LAN, the second-layer switch identifies the sender of the data packet through the source MAC address, and forwards the data packet according to the destination MAC address. For packets whose destination addresses are not on the LAN, the Layer 2 switch cannot send them directly to the destination. It needs to be forwarded through a routing device such as a traditional router. At this point, the switch must be connected to the routing device. If the default gateway of the switch is set to the IP address of the routing device, the switch will send the data packets that need to be forwarded to the routing device through routing.

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The routing device examines the destination address of the packet and its own routing table. If a forwarding path is found in the routing table, the routing device forwards the data packet to other network segments. Otherwise, the packet will be dropped. A dedicated router is expensive, complex, slow, and can easily become a network bottleneck because it needs to analyze all broadcast packets and forward some of them. It also needs to exchange routing information with other routers, and these processes are handled by the CPU (rather than a dedicated ASIC).

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A Layer 3 switch can not only identify and forward data packets by MAC address like a Layer 2 switch, but also route and forward between two network segments like a traditional router. Traditional routers use software to maintain routing tables, while Layer 3 switches handle routing and forwarding through dedicated ASIC chips. Compared with traditional routers, the routing speed of Layer 3 switches is usually ten or dozens of times faster.

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The routing connection of the Layer 3 switch is shown in the figure below