Introduction to layer-3 vswitch technical ports: White Paper by technicians

Introduction to layer-3 Switch technical ports: Many enthusiastic netizens have provided answers to layer-3 Switch technical questions in the White Paper of the technician. Do you have any practical help for the questioner, thank you for your generous support.

The so-called sharing technology means that every workstation on a logical network is in the same network segment. The CSMA/CD mechanism is adopted in Ethernet. This conflict detection method ensures that only one site can be transmitted on the bus. If two sites attempt to access the bus and transmit data at the same time, this means that a "Conflict" occurs and both sites will be notified of an error. Then they are all rejected, and wait for a while for re-sending.

This mechanism is similar to the fact that many cars have snatched a narrow bridge. When the two cars attempt to mount the bridge at the same time, there is a "Conflict" between them. Both cars must exit, and then they start to rush again. When there are too many cars, such unordered competition will greatly reduce efficiency and cause traffic congestion.

The same is true for networks. When the number of users on the network is small, the traffic on the network is light, and there are fewer conflicts. In this case, the conflict detection method works better. When the traffic on the network increases, conflicts also increase, and the throughput of the inbound network will also decrease significantly. When traffic is high, the Workstation may be rejected again and again.

Layer-3 Switching Technology

The layer-3 switch technology is used to provide effective network segment division solutions for shared LAN. It allows each user to share the maximum bandwidth as much as possible. Layer-3 switch technology operates on the data link layer in the OSI Layer-7 network model.

Therefore, the switch forwards data packets based on the MACMedia Access Control Address (physical address). For the IP network protocol, it is transparent, that is, when the switch forwards data packets, if you do not know the IP address of the source machine and the host machine, you only need to know the physical address, that is, the MAC address.

During the operation, the switch will constantly collect data to create an address table of itself. This table is quite simple. It shows the port on which a MAC address is found, when the switch receives a TCP/IP packet, it checks the destination MAC address of the packet and its address table to determine the port from which the packet should be sent.

Because this process is relatively simple, and this feature is implemented by a brand new hardware-ASIC (Application Specific Integrated Circuit), the speed is quite fast, generally only a few dozen microseconds, the switch determines where an IP packet should be sent.

It is worth mentioning that if the switch receives an unknown packet, that is, if the destination MAC address cannot be found in the address table, the switch will "diffuse" the IP address packet, that is, it is sent out from each port, just as when the switch processes a received broadcast packet.

The weakness of a layer-2 switch is that it does not effectively process broadcast packets. For example, when a switch receives a broadcast packet from a TCP/IP workstation, this packet will be sent to all other ports, even if some ports are connected to IPX or DECnet workstation.

In this way, the bandwidth of non-TCP/IP nodes will be negatively affected. Even if the same TCP/IP node has the same subnet as the workstation that sent the broadcast packet, then they will receive some network broadcasts irrelevant to them for no reason, and the efficiency of the entire network will be greatly reduced. LAN switching devices have emerged since 1990s. From the perspective of network switching products, there are roughly three types of switching products: port switching, frame switching, and metadata switching.

Port Switching

The layer-3 port switch technology first appeared in the slot hub. The backplane of such hubs is usually divided into multiple Ethernet segments, each of which is a broadcast domain), and each network segment is connected through a bridge or router. After the Ethernet module is inserted, it is usually allocated to a backplane network segment. Port switching is suitable for allocating Ethernet module ports between multiple network segments of the backplane.

In this way, the network administrator can allocate users between different network segments based on the network load. This layer-3 switch technology is based on the OSI Layer-1 physical layer. It does not change the characteristics of shared transmission media, so it is not a real exchange.

Frame Switching

Frame switching is currently the most widely used layer-3 Switch Technology in LAN. It segments Traditional transmission media and provides a parallel transmission mechanism, reducing collision and conflict domains in the network, to obtain a higher bandwidth. There are differences in the frame exchange technology between products of different manufacturers. However, there are two methods to handle network frames: storage, forwarding, and pass-through.

Store-and-Forward: when a data packet enters a switch using this technology, the switch reads enough information to determine which port will be used to send the data packet, it also determines whether to send the packet. In this way, the defective network segments can be effectively excluded.

Although this method is not as fast as using a straight-through product, it can eliminate the regular and harmful consequences caused by broken data packets. Straight-Through: when a data packet enters a switch using this technology, its address is read. The packet is then sent regardless of whether it is in the wrong format.

This method provides a large number of exchanges because only the first few bytes of the data packet are read. However, all data packets, even those that may have been damaged, will be sent. It is not until the receiving station can detect these corrupted packets and require the sender to resend the packets. However, if the network interface card is invalid, the cable is defective, or there is an external signal source that can cause data packet destruction, the error will be very frequent.

With the development of technology, direct exchange will be gradually eliminated. In the "pass-through" switch mode, the switch only reads the first few bytes of the network frame and then transmits the network frame to the corresponding port. Although the switching speed is fast, however, the lack of advanced control over network frames is not intelligent and secure, nor can it support switching ports with different rates; in contrast, the "Storage and forwarding" switch mode checks and controls the reading of network frames. Lenovo network products all adopt the "Storage forwarding" exchange method.

Cell Switch

The basic idea of cell exchange is to exchange cells with a fixed length, so that hardware can be used for exchange, thus greatly improving the switching speed, especially suitable for the effective transmission of voice, video and other multimedia signals. Currently, the actual application standard of cell switch is the asynchronous transmission mode of ATM. However, the cost of ATM equipment is relatively high. The application in LAN has been gradually replaced by the layer-3 Switch Technology of Ethernet frames.