The difference between a three-tier switch and a router

In recent years, with the rapid development of internet/intranet and the wide application of B/S computing mode, the business of cross region and network has been growing rapidly, and the industry and users have deeply felt the bottleneck effect of traditional routers in the network. The three-layer switch can operate on the third layer of the network protocol, play the role of routing decision, and have the speed of the second layer exchange, and the price is relatively low. For a time, the three-tier switch will replace routers as the most popular topic in the network world. But is that really the case?

Traditional routers in the network have routing forwarding, firewalls, isolated broadcast, and in a network divided into VLAN, the logical division of the different network segments between the communication still to be forwarded through the router.

Because of the large amount of communication data between different VLANs on the local area network, this will become a bottleneck if routers are routed once for each packet, and as the amount of data on the network grows. The third layer switching technology is the technology of combining routing technology with Exchange technology.

After the first data flow is routed, the it will generate a MAC address and IP address mapping table, when the same data flow through again, according to this table directly from the two layer through rather than again routing, thus eliminating the router routing and resulting in network delay, improve the efficiency of packet forwarding.

The forwarding of routers uses the longest matching method to achieve complex, usually using software to achieve. And the three-layer switch routing lookup is for the flow, it uses the cache technology, it is easy to use ASIC implementation, therefore, can greatly save costs, and realize fast forwarding.

However, technically speaking, routers and three-tier switches have significant differences in packet switching operations. Routers typically perform packet switching by a microprocessor based primer, while a three-tier switch performs packet switching through hardware. Therefore, compared with the three-layer switch, the router functions more powerful, such as NAT, VPN and other functions can not be completely replaced.

In the same LAN in the interconnection of each subnet, you can use the three-tier switch to replace the router, but the LAN must be interconnected with the public network to achieve a cross-regional network, then the router is indispensable. A network that is completely built on a switch can have problems such as collisions, congestion, and communication clutter. By using routers to divide a network into multiple subnets, you can avoid these problems by routing the functionality that is available for effective security control strategies.

The three-tier switch does not yet provide a complete routing protocol, and routers have the ability to handle multiple protocols at the same time. When connecting networks of different protocols, such as Ethernet and Token Ring network, it is impossible to transfer data between networks by three-layer switch. In addition, routers also have a fourth layer of network management capabilities, which is not available in the three-tier switch.

Therefore, the three-tier switch is not equal to routers, and it is not possible to completely replace routers.