What is a two-tier switch?

Two-layer switch refers to only the second layer of OSI (data Link Layer) Exchange technology of the switch, the development of two-tier exchange technology is more mature, the two-tier switch is a data link layer equipment, can identify the data packet MAC address information, based on the MAC address forwarding, and record these MAC addresses with the corresponding ports in an internal address table.

Process

(1) When the switch receives a packet from a port, it first reads the source MAC address in the header, so it knows the source MAC address machine is connected to which port;

(2) to read the destination MAC address in the header and find the corresponding port in the Address table;

(3) If there is a port corresponding to the MAC address in the table, copy the packet directly onto the port;

(4) If the table can not find the appropriate port to the packet broadcast to all ports, when the target machine to respond to the source machine, the switch could learn a destination MAC address and which port corresponding, the next time the data transfer will no longer need to broadcast all the ports.

The continuous cycle of this process, for the whole network of MAC address information can be learned, the second-tier switch is to create and maintain its own address table.

Characteristics

From the two-layer switch can be inferred from the operating principle of the following three points: (Small series recommended: What is four-layer switch)

(1) because the switch to the majority of the port data exchange, this requires a very wide exchange bus bandwidth, if the two-tier switch has n ports, each port bandwidth is M, the switch bus bandwidth over NXM, then this switch can achieve wire speed exchange;

(2) Learning port connected Machine MAC address, write Address table, Address table size (generally two representations: one for buffer RAM, one for Mac table item value), Address table size affects the access capacity of the switch;

(3) Another is that a two-tier switch typically contains an ASIC (application specific integrated circuit) chip specifically designed to handle packet forwarding, so the forwarding speed can be very fast. Because each manufacturer uses the ASIC different, the direct influence product performance.