OSI model, tcp/ip model

** One .**OSI Reference model （ Seven layers ）

Switch ：

 Switch （Switch） Meaning for “ switch ” It's used for electricity （ light ） Network equipment for signal forwarding , It can 
 Provide exclusive electrical signal path for any two network nodes connected to the switch . When there are many ports 
 Next , You need to send data to many terminal addresses , The switch is about to be used .

Functionally ： A switch is used to connect multiple devices , Let it have the conditions of network intercommunication .
By definition ： A switch is a network device , Can connect multiple devices to the computer network , By means of packet exchange , Forward data to the destination .

 working principle ：
 The switch works on OSI Reference the second layer of the model , Data link layer . Inside the switch CPU Will be in every 
 When the port is successfully connected , By way of MAC The address corresponds to the port , Form a picture of MAC surface . In future communications 
, Send it to MAC The address packet will only be sent to its corresponding port , Not all the ports . therefore , hand over 
 The switch can be used to divide the data link layer broadcast , The conflict domain ; But it can't divide network layer broadcasting , The broadcast domain .

Router
Two or more devices are connected to a network , Act as a gateway between networks , It's a dedicated intelligent network device that reads the address in each packet and decides how to transmit it . It can understand different agreements , For example, the Ethernet protocol used in a LAN , Used by the Internet TCP/IP agreement . such , The router can analyze the destination address of packets from different types of networks , Turn the non TCP/IP The address of the network is translated into TCP/IP Address , Or vice versa ; Then according to the selected routing algorithm, each packet is transmitted to the designated location according to the best route . So the router can put the non TCP/ IP The Internet is connected to the Internet .
The difference between router and switch ：

1. Using the switch to access the Internet is to dial up separately , Use their own broadband accounts , The Internet does not affect each other .
 The router shares a broadband account , Everyone will interact with each other on the Internet .
2. The switch works in the relay layer , Switch based on MAC Address addressing . Routers work on the network layer , according to 
IP Address addressing .
3. The switch can make multiple computers connected to it form a local area network , If there is a proxy server, it's ok 
 Realize the function of surfing the Internet at the same time , However, the switch does not automatically identify the sending and arrival addresses of packets as the router 
 function .
4. Routers provide services for firewalls . Routers only forward packets of a specific address , No transmission, no support 
 Packet transmission with Routing Protocol .