The number of interfaces on a core switch depends on the number of aggregation switches it connects to, the desired redundancy, and the port speeds, typically ranging from dozens to hundreds of high-speed ports.

Core Switch Interface Considerations

A core switch serves as the backbone of a hierarchical network, aggregating traffic from multiple distribution or aggregation switches rather than connecting directly to end devices . The number of interfaces required depends on:

• Number of aggregation switches: Each aggregation switch typically connects to the core via multiple high-speed links. For example, in a network with six aggregation switches, each might require two 100-GbE links to the core, resulting in 12 core interfaces dedicated to aggregation connectivity .
• Redundancy: Core switches often operate in pairs or clusters to ensure high availability. Dual-core setups allow failover and load balancing, effectively doubling the number of required interfaces for redundancy .
• Port speed and type: Modern core switches support 40-GbE, 100-GbE, or even 400-GbE ports. The choice of port speed affects the total number of physical interfaces needed to handle the network's bandwidth requirements .
• Future scalability: It is recommended to provision extra interfaces to accommodate network growth, additional aggregation switches, or higher bandwidth demands .

Practical Example

Using Fortinet's core layer design as a reference, a core layer may consist of two high-speed switches, each with 32x100-GbE ports, supporting multiple aggregation switches while maintaining redundancy and high throughput . Without a dedicated core, each aggregation switch would require multiple direct links to every other aggregation switch, significantly increasing the total number of interfaces. With a core, the number of required links is reduced, centralizing high-speed connectivity.

Summary

• Minimum: At least two core switches for redundancy.
• Interfaces: Determined by the number of aggregation switches × number of uplinks per switch, plus additional ports for redundancy and future growth.
• Port type: High-speed ports (40/100 GbE) are standard for core connectivity.
• Scalability: Provision extra interfaces to accommodate network expansion and maintain non-blocking performance. In essence, the exact number of interfaces is network-specific, but planning should focus on redundancy, high-speed uplinks, and future scalability to ensure the core switch can handle the full traffic load efficiently .