In Figure 4, we can see a typical deployment with two spines and three leaves. The Nexus 9500 modular switches are deployed at the top of the topology and act as spines, which in a traditional three-tiered network design would be the aggregation or core switches. Line cards are used to provide the ASICs (application-specific integrated circuitry) required for ACI. There are different line cards available, so make sure you are not purchasing a card that is NX-OS mode only.
The next component is the leaf switches. These are the Nexus 9300-series switches.
The spines connect to the leaves through 40 GE ports, but the spines and leaves are never connected (spine to spine or leaf to leaf).
We can also extend the network, ...