Final answer:
The oversubscription ratio is a network design parameter that compares demand to capacity, guiding the number of leaf switches in spine-and-leaf networks. The choice of spine switches considers redundancy and bandwidth needs. Building networks at Layer 2 offers simplicity but increased broadcast risk, whereas Layer 3 promotes scalability and fault isolation but can be complex to manage.
Step-by-step explanation:
The oversubscription ratio refers to the relationship between the potential maximum demand and the actual capacity provided. In network design, particularly in a spine-and-leaf architecture, this ratio helps in determining how many leaf switches are needed by comparing the aggregated access layer bandwidth to the uplink bandwidth from the leaf switches to the spine switches.
An appropriate oversubscription ratio varies, but it is commonly between 3:1 to 5:1 for enterprise networks. The actual selection depends on the expected traffic patterns and the performance requirements of the network. To decide on the number of spine switches, you need to consider redundancy, the number of leaf switches, and the desired path diversity. The required number of uplinks from the leaves, and their available bandwidth, will determine how many spines are needed to support them without exceeding the desired oversubscription ratio.
Building a spine-and-leaf network at layer 2 (VLANs) or layer 3 (subnets) comes with both advantages and disadvantages. Layer 2 facilitates easier VM mobility and can be simpler to manage, but it is more prone to broadcast storms and has a larger failure domain. On the other hand, Layer 3 offers better fault isolation, easier scalability, and no Spanning Tree Protocol overhead, but it can be more complex to configure and manage.