Problem Statement & Context
How Problem Statement & Context shapes architecture and interviewer follow-ups for Design IP Reputation Service.
Problem Statement & Context
Design a global IP reputation platform (Cloudflare/Akamai/Proofpoint class) that scores IPv4/IPv6 addresses and CIDR aggregates for WAF, CDN, email, and SOC consumers. This section focuses on why IP reputation is a shared control plane for edge security products.
- 1.1: shared scoring plane
- 1.2: multi-tenant consumers
- 1.3: longest-prefix match
Mechanism
Every HTTP, SMTP, and API request carries a source IP. A reputation service maintains numeric scores, categories (spam, scan, botnet), and TTL metadata keyed by IP or CIDR. Edge PoPs must answer lookups locally; regional services ingest threat feeds and push versioned snapshots.
Interview phrasing
Open with consumers (WAF, rate limiter, email gateway) and the sub-millisecond lookup budget at PoP.
Failure mode to volunteer
Treating reputation as a nightly batch job—credential stuffing needs second-level feed fusion.
| Signal | Target |
|---|---|
| Peak lookups | 80M |
| IPv4 rows | 4B compressed |
| Feed events/day | 50M |
| Consumers | 6 products |
1 public record ReputationVerdict(int score, String category, long version) {}
1 Verdict = tuple[int, str, int] # score 0-100, category, snapshot version
1 export interface ReputationVerdict { score: number; category: string; version: number; }
Why interviewers care
IP Reputation Service interviews reward crisp scope, explicit trade-offs, and failure stories—not generic microservice diagrams.
Interview checkpoint
Name one failure story for Problem Statement & Context that proves you understand real outages, not happy-path diagrams.
Key Highlights
- •Problem Statement & Context: why IP reputation is a shared control plane for edge security products
- •Mechanism: shared scoring plane
- •Metric anchor: 80M lookups/s / 0.5ms p99
Section Rescue Kit
Buzzwords to use:
Safe statements:
- "For Problem Statement & Context, I anchor 80M lookups/s and 0.5ms p99 before drawing boxes."
- "I never fail-open on known botnet CIDRs—degrade to cached snapshot instead."