In a three-stage IP fabric (also known as a Clos fabric), traffic between any two points (ingress to egress) in the fabric is only two hops away.
Step-by-Step Breakdown:
Three-Stage IP Fabric:
Leaf Layer: Leaf switches connect directly to servers and edge devices.
Spine Layer: Spine switches provide connectivity between leaf switches but do not connect to each other directly.
Two-Hop Communication:
In this architecture, every leaf switch is connected to every spine switch. Therefore, when a packet enters the fabric via an ingress leaf switch, it is forwarded to a spine switch, which then directs the packet to the correct egress leaf switch. This path always involves exactly two hops:
Ingress leaf → Spine → Egress leaf.
Benefits:
This consistent two-hop path ensures predictable latency and makes the network highly scalable while maintaining low complexity.
Juniper Reference:
IP Fabric Architecture: This two-hop property of Clos fabrics is a hallmark of spine-leaf designs, as supported by Juniper's QFX and EX switches in data centers.