Describes how to connect to a layer-3 Switch

A layer-3 switch does have a certain "routing" function, which can implement different subnet connection functions. However, it must be noted that its routing function is much weaker than that of a router, in addition, a layer-3 switch can only use one network.

Generally, it is only the interconnection between LAN subnets that cannot connect the LAN to the WAN or the Internet, because the routing protocols supported by layer-3 switches are very limited. After all, this is not its main function. We know that on the LAN, a layer-2 switch identifies the packet sender through the source MAC address and forwards the packet according to the destination MAC address.

For a data packet whose destination address is not on the local area network, a layer-2 switch cannot directly send it to the destination. It must be forwarded by a routing device (such as a traditional router, connect the vswitch to the routing device. If you set the default gateway of A vswitch as the IP address of the router device, the vswitch sends the packet to be forwarded by the route device.

The routing device checks the destination address of the data packet and its route table. If the route table finds the forwarding path, the routing device forwards the data packet to other network segments. Otherwise, the data packet is discarded. A dedicated router is expensive, complex, slow, and easy to become a network bottleneck because it needs to analyze all the broadcast packets and forward some of them, and exchange route information with other routers, in addition, these processes are all processed by the CPU (not dedicated ASIC ).

A layer-3 switch can identify and forward data packets through a MAC address like a layer-2 switch, and can also forward data packets between two CIDR blocks as a traditional router. Traditional routers use software to maintain route tables, while layer-3 switches use dedicated ASIC chips to process route forwarding. Compared with traditional routers, the routing speed of layer-3 switches is generally 10 times faster or dozens of times faster.

As we all know, a router can connect to an enterprise LAN and a wide area network (such as the Internet), but it ignores another application of a router, that is, its LAN connection function. For details about the WAN connection of a router, see the topology diagram and the router connection diagram of a layer-3 switch.

The role of a vro varies depending on the vro type. Generally, a vro refers to a VBR that is located at the boundaries of different types of networks, as shown in the topology and the router connection diagram of the layer-3 switch. There is also a vro.

It is designed not for connections of different types of networks, but for connections between different LAN or subnets of the same LAN. This is the "intermediate node Router ". Shows its network structure. Compared with the router connection diagram of a layer-3 switch, it uses an intermediate node router to replace the original layer-3 switch.

The "virtual border router" is at the edge or end of the network border and is used to connect different network routers. This is also the type of most routers currently. As described above, the Internet Access Router and the VPN Router to be introduced later belong to the border router. This type of router supports a wide range of network protocols and routing protocols, with extremely high backboard bandwidth and high throughput capabilities to achieve interconnection between different types of networks (including LAN and WAN.

The "intermediate node Router" is located inside the LAN, which is usually used to connect different LAN and serve as a bridge for data forwarding. The intermediate node router pays more attention to the memory performance of the MAC address and requires a large cache. Because the connected network is basically a LAN, the network protocols supported are relatively simple, and the backboard bandwidth is also small, all of which are to achieve the highest cost effectiveness and adapt to the general enterprise's accompanying capabilities.

Compared with the routing function of a layer-3 switch, the routing function is certainly better than that of a layer-3 switch, but in a network with frequent LAN data exchange, using an intermediate node router for LAN connection may affect the network performance.

In general, if the LAN or subnet to be connected is large, network mutual access is not frequent, and the routing is complicated, it is best to use the intermediate node router connection scheme. However, it is best to use a layer-3 Switch Connection Mode in a few scenarios where subnet connections and frequent intercommunication between networks. In addition, it can save equipment investment, because layer-3 switches not only provide routing functions to meet application requirements, but also can be used as switches to connect many network devices.

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