Just wrapped up my Cisco system design loop for a senior SWE role on the enterprise networking side. Wanted to share specifics because the existing posts are pretty thin.
The system design round was 60 minutes, one interviewer, not a panel. The problem I got was essentially: design a real-time network telemetry pipeline that ingests metrics from 100k+ devices and surfaces alerts with sub-minute latency. Pretty fitting for Cisco's domain, which honestly made it easier to stay grounded in realistic numbers.
What they focused on: Data ingestion layer (Kafka came up, I talked about partitioning by device ID and why) Storage tiering: hot path in Redis for live alerting, cold in a time-series DB like InfluxDB or Cassandra for trend queries The alert fanout problem: how do you avoid a thundering herd when 10k devices flip a threshold at once
The interviewer was technical and engaged. He pushed back on my Cassandra choice and asked how I'd handle schema evolution over 5 years of device types. That kind of depth tells you this isn't a rubber-stamp round.
One thing that surprised me: they don't really do the classic "design Twitter" or "design YouTube" style. The prompts lean toward networking infrastructure, security monitoring, or distributed control plane stuff. Makes sense given the product surface, but worth knowing if you're coming from a consumer-company background.
Timing: got about 10 minutes for me to clarify requirements, 30 minutes of diagramming and discussion, then 10 minutes of deep-dive on one component they picked. No coding in this round.
Overall I'd rate it medium-hard. The interviewer was fair, no gotchas. I didn't get the offer (got to final debrief then no) but I thought the design round itself went reasonably well. The behavioral piece of the same day was what tripped me up, I think.
Feel free to ask specific questions.