Which of the following devices do not directly connect to a spine switch? (Choose four.)
- another spine switch
- a router
- a leaf switch
- a server
- an APIC controller
Of the available choices, only a leaf switch can connect to a spine switch. In a spine-leaf architecture, the leaf layer of switches provides connectivity to and scalability for all other devices in the data center network. However, leaf switches do not connect to other leaf switches. Instead, a leaf switch communicates with another leaf switch by using a spine switch. The following exhibit displays a typical spine-leaf architecture wherein the top row of devices represents the spine layer of switches and the bottom row of devices represents the leaf layer of switches:
In the exhibit above, the leaf switches are each directly connected to both spine switches. Switches S1 and S2 comprise the spine layer of the topology. Switches L1, L2, L3, L4, L5, and L6 comprise the leaf layer of the topology. In order for L1 to send a packet to L6, the packet must traverse either S1 or S2. The spine-leaf architecture differs from the traditional three-tier network architecture, which consists of a core layer, an aggregation layer, and an access layer.
Leaf switches connect to spine switches. In a spine-leaf architecture, spine switches are used to provide bandwidth and redundancy for leaf switches. Therefore, spine switches do not connect to devices other than leaf switches. As the name implies, spine switches are the backbone of the architecture.
Leaf switches connect to Cisco Application Policy Infrastructure Controllers (APICs). The leaf switch to which a Cisco APIC is directly connected is the first device in a spine-leaf architecture that will be discovered by and registered with the APIC. When a Cisco APIC begins the switch discovery process, it first detects only the leaf switch to which it is connected. After that leaf switch is registered, the APIC discovers each of the spine switches to which the leaf switch is connected. Spine switches do not automatically register with the APIC. When a spine switch is registered with the APIC, the APIC will discover all the leaf switches that are connected to that spine switch.
Leaf switches connect to routers. Routers are typically used to connect to the Internet or to a wide area network (WAN). Leaf switches in a spine-leaf architecture directly connect to routers.