What is a layer-1 switch, layer-2 switch, and layer-3 switch?

Source: Internet
Author: User

Simply put:

Layer-1 switchOnly physical layer protocols are supported (one phone-controlled switch can be called ???)

L2 SwitchSupports physical layer and data link layer protocols, such as Ethernet switches.

L3 SwitchSupports physical layer, data link layer, and network layer protocols, such as some switches with routing functions.



In terms of the ISO/OSI hierarchy, switches can be divided into L2 switches and L3 switches. A layer-2 Switch refers to a traditional switch that works on the Layer 2 of the OSI benchmark model-data link layer. Its main functions include physical addressing, error verification, frame sequence, and throttling. A pure second-level solution is the cheapest solution, but it provides the least control in terms of dividing subnets and broadcast restrictions. Traditional routers and external switches can also solve the problem, but now the processing speed of the router cannot meet the bandwidth requirements. Therefore, layer-3 switches and Web switches emerged.

A layer-3 switch is a layer-3 Switch with layer-3 routing, not simply overlay the hardware and software of a router device on a LAN switch.

The Web switch provides management, routing, and load balancing transmission for Data Center devices (including internetserver, firewall, quickbuffer server, and gateway. Unlike traditional network devices, traditional network devices focus on quickly completing the exchange of individual frames and data packets, while Web switching failover focuses on tracking and processing web sessions. In addition to the connections and packet routing provided by the traditional second/third-layer switches, the Web switch can also provide the complete policies lacking by the traditional LAN switches and routers, it integrates local and global Server Load balancer, access control, service quality assurance (QOS), bandwidth management, and other management capabilities. Currently, Web switches have evolved from purely transport layer (Layer 4) devices to smart Content-based (Layer 7) switches. Using content or user classification for Web Request redirection is a function of webserver. However, the development of Internet transmission and commerce far exceeds the improvement of computer processing capabilities. Unloading content classification to a Web switch balances the infrastructure of the entire site.



---------------- Layer 3 switches are switches with routing functions !! The two layers are based on the MAC address! -------------------------


There are two common types of vswitches,

One is a layer-2 switch, which we see most,Mac-basedLayer-2 high-speed switching. All interfaces are in the same broadcast domain.


The other is the layer-3 switch you mentioned. As the name suggests, the layer-3 switch can use the routing function. In the early stage, the layer-3 switch requires an msfc (multi-layer switching Feature Card) to supportLayer-3 routing, The modern layer-3 Switch integrates this function.

Example 1 _ Layer 2 Switch:

Two Layer-2 switches are deployed on the first floor of each floor, which can be divided into VLANs for communication. However, assume that the switch on the first floor and the switch on the second floor are not in the same VLAN, and they need to communicate with each other, so they need to use routers for routing.

Example 2 _ layer-3 Switch:

As shown above, assume there are many other floors and many other switches,A three-layer core switch is required to replace the router.


The principle of a layer-3 switch is very easy: one route is used for multiple exchanges.

Explanation: In the wide area network, of course, layer-3 data packets (routed) are run, and the route needs to determine the optimal path from the source to the destination each time, and the route needs to be selected again each time, if you use a layer-3 switch, you can perform the source-to-destination route for the first time. The layer-3 Switch forwards the data to layer-2, or both the source and destination are for high-speed switching.



Layer-3 switches have the routing function, but cannot completely replace the router, because the basic principle is not the same.
In a sense, layer-3 switches are much faster than router policy forwarding!
Layer-3 switches can easily save network resources and prevent congestion.

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