An InfiniBand fabric has no active subnet manager. What is the effect?
Why C is the answer
Ports will not reach the active state, so traffic does not flow
The subnet manager assigns addresses and programs routes, so the fabric cannot carry traffic without one.
In detail
- With no subnet manager, ports do not reach the active state.
- It assigns addresses and programs routes.
Use case
An illustrative scenario, not a real incident.
A new fabric powers on, but ports never go active, because no subnet manager is running.
See it in different ways
flowchart LR A["Discover fabric"] --> B["Assign LIDs"] B --> C["Program routing tables"] C --> D["Ports go Active"] D --> E["Standby SM takes over on failure"]
stateDiagram-v2 [*] --> Down Down --> Initializing: link comes up Initializing --> Armed: SM assigns a LID Armed --> Active: SM finishes the configuration Active --> [*]
flowchart TD
Q{"Is a subnet manager running?"}
Q -->|"No"| A0["Start one"]
Q -->|"Yes"| A1["Check the port"]Key point: No subnet manager means no traffic.
Why the other options are wrong
- A. Only monitoring stops, and links keep carrying traffic as normal
- Traffic stops, not only monitoring.
- B. Links work as normal until the next cable change
- Links do not work as normal.
- D. Only latency increases, because routes are not optimized
- Traffic stops, so latency is not the issue.