How to set up a routing connection for a three-tier switch

The three-tier switch does have a certain "routing" feature that enables different subnet connectivity, but the particular concern is that its routing capabilities are much weaker relative to routers, and that three-tier switches can only use one network.

And it's usually just the interconnection between the LAN subnets, and it's not possible to connect the LAN to the WAN, or the Internet, because the routing protocols supported by the three-tier switch are very limited, which is not the main function. We know that on the LAN, the second-tier switch identifies the sender of the packet through the source MAC address, and forwards the packet based on the destination MAC address. For a packet with a destination address that is not on the local area network, it is not possible for the second-tier switch to send it directly to the destination, which needs to be forwarded via a routing device (such as a traditional router), when the switch is connected to the routing device. If the switch's default gateway is set to the IP address of the routing device, the switch sends packets that need to be routed forward to the routing device. The routing device checks the destination address of the packet and its own routing table, and if a forwarding path is found in the routing table, the routing device forwards the packet to the other network segment, otherwise the packet is discarded. A dedicated router is expensive, complex, slow, and easy to become a network bottleneck, because it analyzes all broadcast packets and forwards a portion of them, as well as exchanging routing information with other routers, and these processes are handled by the CPU (not a dedicated ASIC).

The third-tier switch can identify forwarding packets through MAC addresses as well as two-tier switches, and can route between two network segments as traditional routers do. Traditional routers use software to maintain routing tables, while the three-tier switch handles routing forwarding through a dedicated ASIC chip. Third-tier switches typically have a speed of 10 times or dozens of times times faster than traditional routers.

As we all know, routers can connect enterprise LAN and wide area network (such as Internet), but ignore another application of one router, that is its LAN connection function. The router's WAN connection can be seen on the topology map and the routing connection diagram of the three-tier switch.

The role of routers varies depending on the type of router, which is often referred to as a border router, which is located on the boundaries of different types of networks, such as the topology map and the routing connection diagram of the three-tier switch. There is also a router.

It is designed not for connections of different types of networks, but for connections between different LANs or different subnets on the same LAN, which is the intermediate node router. Its network structure is shown in the following figure. Compared with the routing connection diagram of the three-layer switch, it replaces the original three-tier switch with the intermediate node router only.

The border router is at the edge or end of the network boundary and is used for connections to different network routers, which is also the type of most routers currently. The Internet access router as described earlier and the VPN router that follows are all part of the border router. These routers support a wide range of network protocols and routing protocols, the backplane bandwidth is very high, has a high throughput capacity to meet the various types of network (including LAN and WAN) interconnection.

The "Intermediate node router" is located inside the local area network, which is usually used to connect different LANs and play a role as a bridge for data forwarding. The intermediate node routers pay more attention to the memory energy of MAC address and require large cache. Because the connected network is basically a LAN, so the supported network protocol is relatively single, backplane bandwidth is also small, these are in order to obtain the highest cost-effective, to adapt to the general enterprise with ability.

Compared with the routing function of the three-layer switch, it is certainly stronger than the three-layer switch in the routing function, but in the network with frequent data exchange, the intermediate node router is used to connect the LAN, and the network performance may be affected.

In general, if the connected LAN or subnet more, the network exchange is not very frequent, routing more complex environment, it is best to use the Intermediary node router connection scheme. However, in a few subnet connections, the frequent exchange of visits between the network environment, it is best to use the three-tier switch connection mode. It can also save equipment investment, because the three-tier switch has not only the routing function to meet the application requirements, but also can be used as a switch to connect many network devices.