Point of View: a user can buy a layer-3 switch.

With the development of China's exchange industry, it has also promoted the continuous improvement of the layer-3 switch technology. Today, we mainly talk about how enterprise users buy layer-3 switches. As the core backbone switch, a layer-3 switch is an inevitable choice for campus networks and urban education networks. It can be said that it is the "lifeblood" of Campus Networks and urban education networks, consider the following factors.

Excellent performance is of course the primary factor for selecting a layer-3 Switch. If the packet forwarding speed is too slow and data cannot be synchronized with the lower-layer switch, a network bottleneck will occur, the parameter used to measure the layer-3 Switching Performance of a layer-3 switch is "Mpps" Million Packet Per Second), that is, "millions of packets Per Second", that is, the number of packets that a layer-3 switch can process Per Second. The higher the number, the higher the layer-3 switch performance, of course, the higher the price. When selecting a layer-3 switch, you need to determine the degree of support for line rate Forwarding Based on the current network size and the scale achieved in the future.

"Backboard bandwidth" is also an important indicator for measuring layer-3 switches, and directly affects the overall packet forwarding and data stream processing capabilities. For small and medium-sized campus networks composed of hundreds of computers, dozens of Gbps of Backboard bandwidth can meet application requirements. For campus networks or urban education networks composed of thousands or even tens of thousands of computers, A large three-tier switch that supports hundreds of Gbps is required. In addition, the time difference between the time when the delayed data packet enters the switch and the time when it leaves the switch) and the percentage of frames that cannot be forwarded at the frame drop rate to all the forwarded frames) address Table depth, line congestion, multiple-to-one metrics are also indicators to consider.

Comprehensive Functions

A layer-3 Switch often acts as the backbone network and should be a "multi-user". Generally, the following functions must be supported.

1. Multicast

Multicast is different from unicast point-to-point communication) and broadcast. data can be sent to a group of nodes across network segments, which is of great significance in VOD, video conferencing, and multimedia communication, these applications are the most commonly used functions of CERNET, so we need to pay attention to them.

2. QoS service quality)

"QoS" is short for "Quality of Service". It is a dedicated network communication term. The QoS mechanism can identify the characteristics of packets passing through switches, such as ports, VLAN members, TOS, MAC addresses, IP addresses or subnets, and TCP bandwidth ), different transmission policies can be adopted based on different types of traffic. QoS is also of great significance for multimedia transmission. CERNET often needs to transmit multimedia information. layer-3 switches have QoS service quality control functions, which can allocate different bandwidths to different applications.

3. Supports Filtering

Layer-3 switches should filter frames and packets based on the port number, IP address, and MAC address to implement security mechanisms. For example, if a computer is not certified, it cannot be connected to the campus network or the urban education network.

4. Broadcast Suppression

In some cases, a layer-3 Switch needs to forward a broadcast packet, such as a BootP packet sent by a DHCP client), but cannot allow broadcast packets to be broadcast randomly. Instead, it is limited when the number of broadcast packets exceeds a certain number. In addition to broadcast storms, there are also other types of storms, such as multi-point transmission storms and unknown MAC address spofs. layer-3 switches should also be able to suppress these storms.

5. Support for Port Trunking)

"Port trunk" means that several ports can be bundled together, and it looks like a port. For example, one Mbps port can provide two-way bandwidth of Mbps), and four Mbps ports can provide a bandwidth of up to Mbps if set to the trunk mode of the port, this method improves the uplink bandwidth without adding devices.

6. Support for 802.1d Protocol

802.1d refers to the Spanning Tree Protocol. In large networks, redundant links are often used to ensure network connectivity. That is to say, to prevent network interruptions, one subnet has multiple paths to connect to the network trunk. However, this will form a loop, so that the data is always circulating in the network, thus blocking the network. After the Spanning Tree protocol is used, the switch can detect and eliminate logical loops in the network, without damaging redundancy and ensuring network performance.

7. VLAN Division

VLAN Division is also a feature of many L2 switches. However, L3 switches need to consider whether VLAN implementation standards are common, how VLAN is set, and whether VLANs can be used across devices.

8. Support for traffic control

Traffic control is the ability to control the data traffic of vswitches. HDX and FDX are common traffic control standards. Therefore, it depends on whether layer-3 switches support these standards. General switches can support this function.

9. What protocols are supported?

For the routing protocol, the layer-3 switch in the campus network can basically meet the requirements of the IP protocol and IPX protocol, because other types of protocols are rarely used. For routing protocols, You need to carefully choose whether to support routing protocols for small networks such as RIP, and whether to support suitable routing protocols for large and medium-sized networks such as OSPF. Compatibility with other routing device protocols should also be considered.