The Layer 3 switch is a switch with some router functions, which works in the third layer of the OSI network standard model: the network layer. The most important purpose of the Layer 3 switch is to speed up the data exchange within the large LAN, and its routing function is also for this purpose. It can achieve one-time routing and multiple forwarding.
The network is developing rapidly in terms of scale and speed. In order to meet the requirements of high-speed data transmission and simplifying complex networks that traditional routers do not have, three-layer switches emerge as the times require.
Three differences between Layer 3 switches and routers:
1. Hardware differences
Layer 3 switches forward data through switching chips, while routers forward data through CPU. Therefore, the three-layer switch is slower than the router in network convergence and has weak ability to resist network shock.
2. Differences in data processing methods
The Layer 3 switch forwards a data packet through the CPU, routes for multiple exchanges at a time, and establishes a hardware table entry of the switching chip (mapping table of mac address and IP address) through the ARP protocol. Subsequent messages are directly forwarded through the switching chip, that is, “one route, multiple exchanges”. The hardware layer 3 table entry of the switch only contains the destination address, destination IP or the mac address corresponding to the next hop IP address Exit VLAN and port.
After the router selects a route through the route table, the route table sends the active route to the FIB (forwarding information table) table. When the data arrives at the router, it is forwarded through the longest matching principle of the FIB table. Therefore, the data forwarding speed of the Layer 3 switch is better than that of the router.
3. Functional differences
Routers provide such functions as packet filtering, packet forwarding, priority, multiplexing, encryption, compression, and firewall. They also have rich interface types, support powerful three-layer functions, support load sharing, link backup, NAT conversion, and exchange routing information with other networks. The router’s protocol calculation, routing table size, and convergence time in large networks are better than those in three-layer switches.
In addition, the advantages of the Layer 3 switch will be introduced:
The advantage of the Layer 3 switch is that it can speed up the data exchange in the LAN, and the routing function is also added for this purpose. Due to the large amount of Internet mutual access in the LAN, the use of Layer 2 switches alone cannot achieve mutual access between different networks. For example, the use of routers alone will limit the network speed and network scale due to interface restrictions and low routing forwarding efficiency. The use of Layer 3 switches with routing functions will become the first choice.
The main purpose of the Layer 3 switch is to replace the traditional router as the core of the network. Therefore, Layer 3 switches can be used wherever there is no need for WAN connection and routing. In LAN, the three-layer switch is generally used in the core layer and convergence layer of the network.
