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The switch forwarding address table
Forwarding may be performed a plurality of switch operations simultaneously
Since hubs broadcast signals intact just go out , so even if the signal is subject to interference noise distortion occurs , it will be as it is sent to the destination . In this case , the device receives the signal , i.e. switches , routers , servers, etc. , will pass after converting the signal into digital information discovery FCSA error checking , and the discarding error packets . Of course , the packet is discarded and does not affect the transmission of data packets discarded since the acknowledgment response is not triggered . Thus stack TCP module packet loss is detected , and retransmission of the packet.
The switch forwarding address table
Signal reaches the cable interface , by a PHY ( the MAU ) module for receiving , and the hub part are the same . That is , its interface, and a PHY ( the MAU ) modules are to MDI-X connection mode B , when the signal incoming from the twisted pair , will enter a PHY ( receiving portion of the module the MAU) .
Next , a PHY ( the MAU ) signal conversion module in the cable will be a common format , and then transmitted to the MAC module . MAC module signals into digital information , and then through the end of the packet FCS checksum error , if there is no problem then is stored in the buffer C . This part of the operation and substantially the same card , can be considered the rear of each cable interface of the switch is a network card . Circuit portion and a rear cable interface together called a port , that is equivalent to a switch port on a computer network card (in other words, if multiple network cards installed on the computer and open "promiscuous mode" let card to receive all the network packets, and then install a network packet switch with the same function forwarding software, this computer becomes a switch) .
The switch works and the card is a little different . Card itself has MAC address , and checking packets received by the receiver MAC address is determined not sent to their own , if not addressed to itself is discarded ; relatively switch port does not check the receiver MAC address , but All packets received direct and place the buffer . Accordingly , and different card , the port does not have a switch MAC address . After the packet into the buffer , then you need to check what the recipient of this package if the MAC address is already in the MAC record the address table . MAC address table contains two main information , is a device MAC address , and the other is connected to the device on which port on the switch . MAC addresses and ports is one to one ,By this table it can be judged that the received packet should be forwarded to which port .
Maintains a MAC address table
During the switch forwarding packet , also the need for MAC to maintain the contents of the address table, maintenance operations are divided into two kinds .
The first is when a packet is received , the sender MAC address and its input port number written in the MAC address table . Since the port that received the packet and even then the equipment sending this packet , so long as the sender of the packet MAC address of the address table written later when receiving the packet sent to this address when , the switch may forward it to is the correct port . This operation is performed every time the switch when the packet is received , so long as a device packet transmitted over the network , its MAC address will be recorded in the address table .
The second is the deletion of a record in the address table , which is to prevent problems when the device moves . For example , we will get a laptop from a desk in the meeting room , this time on the device has been moved . From the point of view of the switch , that would have been connected to a port of the laptop disappeared . Then if the switch received the sent this has disappeared laptop bag , it still forwards the packets to the original port , a communication error occurs , it is necessary to find a way to delete outdated records . However , the switch is no way to know this laptop has been removed from the original port . Thus recording address table is not permanent , but rather in a
Period of time is not automatically deleted after use. Outdated recording time deleted from the address table is generally a few minutes , so before stale record is deleted , may still have the package sent to the device arrives at the switch . At this time , the switch forwards the packets to the old port , a communication error occurs , this situation although rare , but it does also happen . But we need to fear , encountered such a situation , just restart the switch , the address table will be emptied and update the correct information , and then on another network can work properly .
In short , the switch will address itself to update or delete records in the table , does not require manual maintenance A. When the content of the address table appears abnormal , just restart the switch can reset the address table does not require manual maintenance .
Forwarding may be performed a plurality of switch operations simultaneously
Switches only forward packets having the particular MAC port connected to the device address , when the packet transmission port from the top to the bottom port , other ports are idle , these ports may transmit other packets , so the switch can simultaneously forwarding multiple packages . Relatively , the signal will broadcast hub inputs to all ports , while if a plurality of input signals will collide , unable to transmit multiple signals simultaneously , and therefore from the point of view of the overall apparatus forwarding capability , the switch than the hub .
Network packets through the router is will happen then? What router is it? -------> https://blog.csdn.net/HYZX_9987/article/details/103877330
