Code Room
On-callHardoc-g678
Subject Networking bgpLevel Senior–Staff~40 minCommon in Networking & APIs interviewsIndustries Technology, Telecom

Question

At 02:14 your edge starts dropping ~30% of inbound traffic for users in Europe; the rest of the world is fine. Synthetic probes from EU vantage points time out before reaching your edge IPs, while probes from US/APAC succeed. Your edge servers show a sharp drop in connections from EU ASNs but are otherwise healthy. A network engineer pushed a routing/peering change ~15 minutes before the incident: a BGP prefix announcement was adjusted to shift EU traffic onto a new transit provider. Traceroutes from affected EU networks die a few hops in, in the new transit's network. Walk through triage, mitigation, and prevention.

What a strong answer looks like

Stop the bleeding first (mitigate), then form hypotheses from real signals. Separate root cause from symptom, communicate status as you go, and close with what prevents a repeat.

Diagram & narrate the incident
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Run or narrate your approach, then ask the coach.