1. Backplane bandwidth
Backplane bandwidth, also known as switching capacity, is the maximum amount of data that can be handled between the switch's interface processor or interface card and the data bus, just like the sum of the lanes owned by an overpass. Since all ports need to communicate with each other through the backplane, the bandwidth provided by the backplane becomes a bottleneck for concurrent communication between ports.
The larger the bandwidth, the greater the available bandwidth provided to each port, and the greater the data exchange speed; The smaller the bandwidth, the less available bandwidth is available to each port, and the slower the data exchange speed. In other words, the bandwidth of the backplane determines the data processing capability of the switch, and the higher the bandwidth of the backplane, the stronger the ability to process data. In order to achieve full-duplex non-blocking transmission of the network, the minimum backplane bandwidth requirement must be met.
The calculation formula is as follows
背板带宽=端口数量×端口速率×2 
Note: For Layer 3 switches, only when the forwarding rate and backplane bandwidth meet the minimum requirements are qualified switches, and both are indispensable.
For example
How a switch has 24 ports,
背板带宽=24*1000*2/1000=48Gbps。 Packet forwarding rates at Layer 2, Layer 2, and Layer 3
The data in the network is made up of individual packets, and the processing of each packet consumes resources. Forwarding rate (also known as throughput) refers to the number of packets that pass through a unit of time without packet loss. Throughput is like the traffic flow of an overpass, which is the most important parameter of a Layer 3 switch, marking the specific performance of the switch. If the throughput is too small, it will become a network bottleneck, negatively impacting the transmission efficiency of the entire network. The switch should be able to achieve wire-speed switching, that is, the switching rate reaches the data transmission speed on the transmission line, so as to eliminate the switching bottleneck to the greatest extent. For Layer 3 core switches, if you want to achieve non-blocking transmission of the network, this rate can ≤ the nominal Layer 2 packet forwarding rate and the rate can ≤ the nominal Layer 3 packet forwarding rate, then the switch can achieve line speed when doing Layer 2 and Layer 3 switching.
Then the formula is as follows
吞吐量（Mpps）=万兆位端口数量×14.88 Mpps+千兆位端口数量×1.488 Mpps+百兆位端口数量×0.1488 Mpps。 If the calculated throughput is less than the throughput of your switch, then it can achieve line speed.
If there are 10 Gigabit ports and 100 Gigabit ports, they will be counted, and if they don't, they don't need to be counted.
For a switch with 24 Gigabit ports, the full-configuration throughput should reach 24×1.488 Mpps = 35.71 Mpps to ensure non-blocking packet switching at average speed on all ports. Similarly, if a switch can provide up to 176 Gigabit ports, it should have a throughput of at least 261.8 Mbps (176×1.488 Mpps = 261.8 Mpps) for a true non-blocking fabric design.
So, how do you get 1.488Mpps?
Packet forwarding line speed is measured based on the number of packets (minimum packets) sent in a unit of 64 bytes. For Gigabit Ethernet, the calculation method is as follows: 1,000,000,000bps/8bit/(64+8+12)byte=1,488,095pps Note: When the Ethernet frame is 64 bytes, you need to consider the fixed overhead of 8 bytes of the frame header and 12 bytes of frame gap.
Thus, a wire-speed Gigabit Ethernet port has a packet forwarding rate of 1.488Mpps when forwarding 64byte packets. Fast Ethernet has a packet forwarding rate of exactly one-tenth that of Gigabit Ethernet, at 148.8kpps.
- For 10 Gigabit Ethernet, the packet forwarding rate for one wire-rate port is 14.88Mpps.
- For Gigabit Ethernet, the packet forwarding rate for one wire-rate port is 1.488Mpps.
- For Fast Ethernet, the packet forwarding rate for one wire-rate port is 0.1488Mpps.
We can use this data.
Therefore, if the above three conditions (backplane bandwidth and packet forwarding rate) can be met, then we can say that this core switch is truly linear and non-blocking.
Generally, a switch that satisfies both is a qualified switch.
Switches with relatively large backplanes and relatively small throughput, in addition to retaining the ability to upgrade and expand, have problems with software efficiency/dedicated chip circuit design; The backplate is relatively small. Switches with relatively high throughput have high overall performance. However, the backplane bandwidth can be trusted by the manufacturer's propaganda, but the throughput cannot be believed by the manufacturer's propaganda, because the latter is a design value, and the test is very difficult and not very meaningful.
3. Scalability
Scalability should include two aspects:
1. Number of slots: Slots are used to install various functional modules and interface modules. Since the number of ports provided by each interface module is certain, the number of slots fundamentally determines the number of ports that the switch can hold. In addition, all functional modules (such as super engine module, IP voice module, extended service module, network monitoring module, security service module, etc.) need to occupy a slot, so the number of slots fundamentally determines the scalability of the switch.
2. Module type: There is no doubt that the more module types supported (such as LAN interface module, WAN interface module, ATM interface module, extended function module, etc.), the stronger the scalability of the switch. Taking the LAN interface module as an example, it should include RJ-45 module, GBIC module, SFP module, 10Gbps module, etc., to meet the needs of complex environments and network applications in large and medium-sized networks.
Fourth, four-layer exchange
Layer 4 switching is used to enable fast access to network services. In Layer 4 switching, the transmission is determined not only by the MAC address (Layer 2 bridge) or source/destination address (Layer 3 routing), but also by the TCP/UDP (Layer 4) application port number, which is designed for high-speed intranet applications. In addition to load balancing, Layer 4 switching also supports transport flow control based on application type and user ID. In addition, the Layer 4 switch sits directly in front of the server and is aware of application session content and user permissions, making it ideal for preventing unauthorized access to the server.
5. Module redundancy
Redundancy is the guarantee of safe operation of the network. No manufacturer can guarantee that its products will not fail during operation. In the event of a fault, the ability to switch quickly depends on the redundancy of the equipment. For the core switch, important components should have redundancy capabilities, such as management module redundancy, power supply redundancy, etc., so as to ensure the stable operation of the network to the greatest extent.
6. Route redundancy
When one of the core switches and dual aggregation switches fails, the Layer 3 routing devices and virtual gateways can be quickly switched to implement redundant backup of the two lines and ensure the stability of the entire network.
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