Spine Leaf and Campus Architectures

Cisco defines two types of architectures for enterprise networks: campus and spine/leaf. It documents 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 leaf switches, we can easily predict the data flow. In this design, traffic always takes the same path:
Leaf -> Spine -> Leaf.

spine leaf design

Since everything is three hops away, administrators can easily load-balance the traffic in the routing table via equal-cost load balancing (ECMP). Besides this, it is also easy to expand the network. If the network needs more ports, administrators add a leaf switch. If it needs more bandwidth, they 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.
  • Each spine switch must connect to every leaf switch.
  • Spine switches cannot connect to each other.

The campus architecture

campus design

The campus architecture is mainly used in traditional enterprise networks.

In this architecture, switches are hierarchically connected to each other. The hierarchical design makes troubleshooting easy since the stuff that belongs in each layer is well-defined.

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 2 interfaces with the access layer switches to terminate the VLANs, and layer 3 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 doesn’t offer any other services.

ComputerNetworkingNotes CCNA Study Guide Spine Leaf and Campus Architectures