What does ECN do on a RoCE network?
Why C is the answer
Marks packets, so senders slow down
ECN signals congestion before buffers fill.
In detail
- ECN signals congestion before buffers fill.
- It acts before buffers fill.
Use case
An illustrative scenario, not a real incident.
A switch marks packets as queues grow, and senders slow down before loss.
See it in different ways
flowchart LR A["RoCE traffic"] --> B["QoS class"] B --> C["ECN signals congestion"] C --> D["PFC prevents drops"] D --> E["Adaptive routing spreads load"]
sequenceDiagram participant S as Sender participant W as Switch participant R as Receiver S->>W: RDMA traffic W->>R: Marks packets with ECN R-->>S: Congestion notification S->>S: Slows down W-->>S: PFC pause, if a queue fills
sequenceDiagram participant P0 as Sender participant P1 as Switch participant P2 as Receiver P0->>P1: Packets P1->>P2: Marked packets P2-->>P0: Congestion notice
Key point: ECN marks packets to slow senders.
Why the other options are wrong
- A. Assigns IP addresses to every new RDMA interface
- It does not assign addresses.
- B. Stops all traffic on a port for a set time
- That describes a pause.
- D. Encrypts traffic between each pair of switches
- It does not encrypt.