Describes the concept and principle of exchange in detail.

Switching is a simple action to move a group (or frame) from one port to another. The decision on how to make a move determines whether a vswitch or a router is used. If you are using the second layer of the OSI model, you need to use a switch or a bridge. If you are using the third layer of the OSI model, you need to use a router or a third layer switch ).

MAC address:　

The data link layer consists of two sub-layers: Logical Link Control (LLC) and Media Access Control (MAC ). The MAC Sub-layer determines the hardware address of the layer, which is irrelevant to the network, so no matter where the hardware is inserted to the network, it has the same MAC address (that is, the MAC address does not change with the network), regardless of the network address. The supplier usually specifies the MAC address of the product. In the Ethernet policy, a series of Ethernet MAC addresses are assigned to the supplier, and then they are assigned to each interface in the production process.

The Ethernet MAC address contains 12 digits. The first six digits (organization identifier or OUI) are the specific numbers assigned to the supplier by IEEE, and the remaining six digits are series numbers. The result is that each network interface plug-in can have different MAC addresses on any given LAN or wide area network.

Switching Principle:

The MAC address table shows the MAC ing between the MAC address of the host and the port of the Ethernet switch, indicating the direction of the data frame to the destination host. When an Ethernet switch receives a data frame, it finds and matches the destination MAC address of the received data frame with the MAC address table. If no matching item exists in the MAC address table, the data frame is broadcast to all ports except the acceptor port. Someone translates this operation into a Flood, the flood operation broadcasts normal data frames instead of broadcast frames ). Some of the switches we have tested can restrict the forwarding of broadcast frames and pan-flood.

When a match exists in the MAC address table, the vswitch port specified by this match is the same as the receiving port, indicating that the destination host and source host of the data frame are in the same broadcast domain, if you do not use a vswitch to complete communication, the vswitch discards the data frame. Otherwise, the switch forwards the data frame to the corresponding port.

The switch also checks the source MAC address of the received data frame and finds the matched items in the MAC address table. If no, the switch records the MAC address and the port that receives the data frame, and activates a timer. This process is called address learning. Due to limited physical memory, all switches can only learn a small subset of the 48 power of 2, so the switch only learns the different devices of different manufacturers with different active MAC addresses, the MAC address capacity is also different, And the MAC address capacity is also an important indicator of the switch). This timer is generally the Age Time option when we configure the switch, generally, we can configure the timer length. When the timer arrives, the record will be deleted from the MAC address table, which is called Aging ). If the source MAC address of the received data frame matches in the MAC address table, the switch resets the timer of this address.

If the vswitch cannot properly learn the MAC address, packet loss and flooding may occur. In particular, a large number of flooding images may affect the forwarding performance of the vswitch, similar to the impact of broadcast storms on vswitches.

1. Detailed description of the principle of layer-3 Switching Technology
2. Basic Principles of Exchange Technology