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Author: Admin | 2025-04-28
Spine switch. Figure 13. As the queue on Leaf X continues to build up, the leaf switch generates a PFC frame to Spine 1 and stop sending traffic to Host X To prevent packet drops, PFC slows down traffic from the spine switch down to Leaf X, and this prevents the leaf switch from dropping traffic. This triggers further buffer utilization on the spine switch. The spine switch experiences a buildup of buffer utilization until it reaches the xOFF threshold, which triggers a PFC frame from the spine switch down to the leaf switches where the senders are connected. Figure 14. Spine 1 generates a PFC frame to Leaf 1 and 2 The leaf switches closest to each sender receive the PFC pause frame and start buffering traffic. The buffer starts building up, and after crossing the WRED threshold traffic, the buffer is marked with ECN, but continues to build as it did in the previous example. After the xOFF threshold on the leaf switches is reached, the system generates a pause frame toward the senders, which further reduces the rate from senders and prevents packet drops. Figure 15. Leaf 1 and Leaf 2 send PFC frames down to hosts A and B, which mitigates congestion As stated previously, using ECN and PFC together is the recommended approach for this blueprint. In the next section, we explore using approximate fair drop (AFD). Using Approximate Fair Drop (AFD) Another way of managing congestion is using advanced QoS algorithms. Cisco Nexus 9000
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