According to OSI's seven-tier network model, the switch can be divided into two-tier switches, three switches. According to the protocol supported by the switch, there are less common four-layer switches and seven-layer switches. The Layer 2 switch, which is based on MAC addresses, is the most common for network access and aggregation. Layer 3 switches based on IP addresses and protocols are commonly used at the core of the network and are also used in aggregation layers. Part of the third layer switch also has a fourth layer switching function, according to the data frame protocol port information to determine the target port. The fourth floor of the switch called the content-based switches, mainly for the Internet data center.

Layer 2 switchs

The Layer 2 switch operates on Layer 2 (data link layer) of the OSI model, identifies the MAC address information in the packet, forwards it according to the MAC address, and records the MAC address and the corresponding port in an address table in. As a result, Layer 2 switches require strong data identification and forwarding capabilities.

Layer 3 switches

Layer 3 switch is a special kind of router, is a performance on the focus on the exchange and low cost of the router. Traditional switching technology is in the OSI network standard model second layer - the data link layer to operate, and three switches is designed for the IP, the interface type is simple, has a strong two-tier packet processing capabilities, it can work in the agreement The third layer replaces or partially completes the functionality of the traditional router, and has the speed of almost the second tier exchange, and the price is relatively cheap.

The most important purpose of the three-tier exchange is to speed up the exchange of data within a large LAN, so that a route, multiple forwarding. When a large local area network in accordance with the functional or geographical factors into a small local area network, VLAN (Virtual Local Area Network Virtual LAN) technology in the network to be a large number of applications, and the communication between different VLANs have to go through the router to complete the forwarding. Simply use the router to achieve not only a limited number of ports, and routing speed is slow, thus limiting the size of the network and access speed.

Layer 4 switchs

A simple definition of the fourth layer exchange is that it is a function that determines that the transmission is based not only on the MAC address (Layer 2 bridge) or source / destination IP address (Layer 3 routing), but also on TCP / UDP Fourth layer) application port number. The fourth layer exchange function is like a virtual IP, pointing to the physical server. It communicates the business to a variety of protocols, including HTTP, FTP, NFS, Telnet or other protocols. These services on the basis of physical servers, the need for complex load balancing algorithm.

When a user requests an application, a VIP connection request with a target server group (such as a TCP SYN packet) is sent to the server switch. The server switch selects the best server in the group, replaces the VIP in the terminal address with the IP of the actual server, and passes the connection request to the server. In this way, all packets in the same interval are mapped by the server switch and transmitted between the user and the same server.