The difference between layer 3 switch and router

      Although they all have routing function , But the main function of the three-layer switch is still data exchange , Its routing function is usually relatively simple , Because it is mainly faced with a simple LAN connection , Routing paths are far less complex than routers , Its main purpose in LAN is to provide fast data exchange function , Meet the application characteristics of frequent data exchange in LAN . 

      The main function of the router is the routing function , Its routing function is more reflected in the interconnection between different types of Networks , Such as the connection between LAN and wan 、 Connection between networks with different protocols, etc , Therefore, routers are mainly used between different types of networks . Its main function is routing and forwarding , Solving the connection of various complex routing path networks is its ultimate goal , So the routing function of router is usually very powerful , It is not only suitable for LAN with the same protocol , It is more suitable for LAN and WAN with different protocols . Its advantage is to choose the best route 、 Load sharing 、 Link backup and routing information exchange with other networks and other router functions . To connect to all kinds of networks , There are many types of router interfaces , And layer 3 switch is only the same type of LAN interface , It's simple .   

      Technically speaking , There are obvious differences between router and layer 3 switch in packet switching operation . Routers are usually implemented by software routing engines based on microprocessors , The layer-3 switch performs packet switching through hardware . The layer 3 switch routes the first data stream , It will produce a MAC Address and IP A map of addresses (MLS), When the same data stream passes again , It will pass through layer 2 directly according to this table instead of routing again , Thus, the network delay caused by router routing is eliminated , It improves the efficiency of packet forwarding . meanwhile , The routing lookup of layer 3 switch is for data flow , It uses caching technology , It's easy to use ASIC Technology to implement , therefore , Can greatly save costs , And realize fast forwarding . The router's forwarding adopts the longest matching method , The implementation is complex , Software is usually used to implement , Low forwarding efficiency . 

Because of this , In terms of overall performance , The performance of layer 3 switch is much better than that of router , It is very suitable for LAN with frequent data exchange ; The router is very powerful , But its packet forwarding efficiency is far lower than that of layer 3 switch , It is more suitable for the interconnection of different types of networks with less frequent data exchange , Such as the interconnection of LAN and Internet . If the router , Especially high-end routers are used in LAN , To a considerable extent, it is a waste （ In terms of its powerful routing function ）, And it can not well meet the requirements of LAN communication performance , Affect the normal communication between subnets  

      in summary , Multi subnet connection in LAN , It's better to use three-layer switch , Especially in the environment of frequent data exchange between different subnets . On the one hand, it can ensure the communication performance requirements between subnets , On the other hand, it saves the investment of buying another switch . Of course , If the communication between subnets is not very frequent , There's nothing wrong with using routers , It can also achieve the purpose of safe isolation and mutual communication of subnetworks . The details should be determined according to the actual needs . 

      The biggest difference between layer 3 switching and routing is ： Routing support nat transformation , The third tier does not support . It is reflected in the actual project ： The route is directly connected to the optical fiber to access the Internet , However, connecting the optical fiber to the layer 3 device can't access the Internet . Each port on the third floor has a dedicated mac Address , There are special ones ASIC The integrated circuit .