Data centre switches and routers are the high-capacity network equipment that carries traffic between the thousands of servers in a data centre, and between the data centre and the outside world. A switch joins many devices inside one network and passes each packet of data to the right device. A router joins different networks and chooses the path that each packet takes between them.
Most data centres arrange their switches in a design called leaf-spine. Each rack has one or two leaf switches at the top, joined to every server in the rack. Every leaf switch is then joined to every spine switch. So any server can reach a server in another rack through exactly three switches: its own leaf switch, one spine switch and the other server's leaf switch. If one spine switch fails, the traffic goes through another spine. This is redundancy, and it also keeps the delay between any two servers short and nearly equal.
Imagine a food delivery app's data centre in Bengaluru at dinner time on a Saturday. Say 3 lakh people open the app within an hour. Each order sets off many messages inside the building: between the web servers, the restaurant database, the payment servers and the storage systems. The data centre has 40 racks, each with two leaf switches, and 8 spine switches above them. Each server has two links of 25 gigabits per second, one to each leaf switch in its rack. At 8:30 p.m., one leaf switch fails. Every server in that rack keeps working over its link to the second leaf switch, and nobody ordering dinner notices.
Speeds are now very high. Leaf switches connect servers at 25, 100 or 200 gigabits per second, and spine switches connect at 400 or 800 gigabits per second. The main chip inside a switch, which decides where each packet goes, comes from a small number of networking chip makers.
At the edge of the data centre, routers connect the building to telecom operators and to other data centres. A load balancer spreads incoming requests across many servers. Network TAPs and packet brokers copy the traffic for security and monitoring tools.
A branded data centre switch comes with its maker's own operating system. Some large buyers instead buy plain hardware and run software from another company, which is called white-box networking. Data centre switches also differ from the enterprise switches in an office. Those connect laptops, phones and Wi-Fi access points, at lower speeds.