Switch theory knowledge

What is a switch
A switch is the main device used to connect a local area network. The switch
can intelligently forward data to the destination address in an Ethernet frame. This switch works at the data link layer. The switch
divides the collision domain and realizes duplex communication . The source mac address of the frame forms the mac address table Broadcast: if the destination address is not in the mac address table, the switch broadcasts the data frame to all other ports except the source port of the data frame . Forwarding: the switch forwards the data frame according to the mac address. The aging time of updating the switch's mac address table is 300 seconds. If a frame is found to be different from the port where the source mac address in the mac address table is located, the switch will relearn the mac address to the new port. Collision domain and broadcast domain Internal switching mode of the switch: storage Forwarding - the most widely used error detection speed is slow Fast forwarding - fast speed, can't troubleshoot segmentation filtering - check whether the length of the data packet is 64 bytes less than 64, it means that it is a fake packet greater than 64, and no number check is provided Ethernet/Working Principle Ethernet adopts CSMA/CD-Carrier Sense Multiple Access with Conflict Detection-Avoiding Signal Conflict Working Principle: Monitor whether the channel is idle before sending, if it is idle, send directly, if there is a conflict, stop sending, Wait for a period of time to continue sending the Ethernet MAC address - it is used to identify an individual device or a group of devices on the Ethernet. The first 8 digits are the manufacturer number provided by IEEE (Institute of Electronics and Electrical Engineering), the last 24 digits are the device number Ethernet frame format destination address source address type data frame validation sequence




















6 bytes 6 bytes 2 bytes 46-1500 bytes 4 bytes
Data link layer sublayer:
Logical Link Control Layer (LLC): Provides an interface with the upper layer, adds sequence numbers to frames, establishes and releases data links The logical connection of the road layer is the
medium access control layer (MAC): Error detection MAC addressing realizes and maintains the control protocol of medium access. It accepts upper layer data and encapsulates it into frames for transmission.