Spine Leaf and Campus Architectures

Cisco documentation defines two types of architectures for enterprise networks: campus and spine/leaf. It lists the campus architecture for traditional networks and the spine/leaf for controller-based networks.

Spine/Leaf Architecture

Cisco uses a specific physical switch topology called spine and leaf for controller-based networks and data centers. It is also known as CLOS design. The term CLOS has no special meaning. It is the name of the creator of this design.

The spine/leaf or CLOS design classifies all switches into two types: spine and leaf. The spine switch provides super-fast transport across the leaf switches. It works as the core layer. It connects leaf switches. The leaf switches connect end devices. Each leaf switch has a high-bandwidth uplink to each spine switch.

Since leaf switches can connect only with spine switches, not with other leaf switches, you can easily predict the data flow. In this design, traffic always takes the same path.

Leaf -> Spine -> Leaf

Since everything is three hops away, you can easily load-balance the traffic in the routing table via equal-cost load balancing (ECMP). Additionally, it is easy to expand the network. If the network needs more ports, you can add a leaf switch. If it needs more bandwidth, you can add another spine switch.

Key points

• End devices connect only to the leaf switches.
• Each leaf switch must connect to every spine switch.
• Leaf switches cannot connect to each other directly.
• Each spine switch must connect to every leaf switch.
• Spine switches cannot connect to each other directly.

The campus architecture

The campus architecture is mainly used in traditional enterprise networks. In this architecture, switches are hierarchically connected to each other. Components that belong in each layer are well-defined. It makes troubleshooting easy.

The campus architecture divides the network into three layers: access, distribution, and core.

The Access layer is the bottom layer of this architecture. It connects end devices. Port-level features like port security and VLANs are configured and applied at this layer.

The Distribution layer is the middle layer of this architecture. It provides routing and IP-based services. A distribution switch uses layer two interfaces with the access layer switches to terminate the VLANs, and layer three interfaces to connect to the core switches.

The Core layer is the top layer of this architecture. It provides high-speed routing between the distribution switches. Besides switching data packets at the fastest possible speed, it does not offer any other services.

Conclusion

The spine/leaf architecture offers a scalable and efficient topology with clear traffic paths and easy load balancing. This design simplifies the expansion of networks while ensuring high bandwidth through dedicated connections between spine and leaf switches. On the other hand, the campus architecture is tailored for traditional enterprise environments, employing a hierarchical structure that enhances troubleshooting and management. With its distinct access, distribution, and core layers, this architecture provides a framework for implementing essential services and configurations, streamlining connectivity from end devices to core routing. Both architectures provide unique benefits, allowing organizations to choose the most suitable design based on their specific requirements and operational goals.