Forward Networks Software Engineer Interview: Longest Prefix Match Problem
Interview Experience
2 Rounds Round 1 Onilne Assesment Round 2 A network device maintains Policy Based Routing (PBR) entries. Each entry contains an IP subnet in CIDR notation and a corresponding next-hop IP address. When
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2 Rounds Round 1 Onilne Assesment Round 2 A network device maintains Policy Based Routing (PBR) entries. Each entry contains an IP subnet in CIDR notation and a corresponding next-hop IP address. When a packet with a destination IP arrives, the device must determine the next-hop based on the Longest Prefix Match rule. If multiple subnets match the destination IP, the subnet with the largest prefix length must be selected. If no subnet matches, the default route (0.0.0.0/0) should be used. You are given: A list of PBR entries represented by a class PrefixEntry, where: ipSubnet is a subnet in CIDR format (e.g., "168.19.100.0/24") nextHop is the next-hop IP address. A list of IPv4 addresses. Write a function: public static Map
Example Prefix entries: 168.19.100.34/32 → 1.1.1.1 168.19.100.0/25 → 1.1.1.2 168.19.100.0/24 → 1.1.1.3 168.0.0.0/8 → 1.1.1.4 0.0.0.0/0 → 1.1.1.5 IP addresses: 168.19.100.34 168.19.100.198 169.0.0.0 Expected output: 168.19.100.34 → 1.1.1.1 168.19.100.198 → 1.1.1.3 169.0.0.0 → 1.1.1.5 Could not Understand what to do, how to do, did my best, but something was off with this question, had to ask interviewer to spare me and wasting his time
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This is a candidate experience report from a forward networks interview for a swe role reported in 2026.
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This question was reported by a candidate who interviewed at Forward Networks. LeakCode aggregates interview reports from 10+ sources, including 1Point3Acres, Glassdoor, LeetCode Discuss, Blind, Reddit, Indeed, and Nowcoder. Each report is translated where necessary, deduplicated against existing entries, and tagged by company, role, round type, and reporting date.
Use this question as one calibration data point, not a memorization target. Companies typically rotate their question pools every 2-4 months; the exact wording of a 2024 question may differ from what you encounter today. The underlying pattern, difficulty level, and follow-up depth at Forward Networks are the higher-signal extractions to take from this report.
For broader preparation context, the Forward Networks interview process typically includes a recruiter screen, one or two technical phone screens, and a 4-5 round on-site loop covering coding, system design (at L4+ levels), and behavioral. Reports tagged on LeakCode show the round-by-round distribution and typical difficulty calibration. To browse questions filtered by round type and seniority, use the company hub linked above.
How To Practice This Type of Question
Solve similar problems on LeetCode under timed conditions (25-35 minutes per medium difficulty). The goal is pattern recognition: recognize the underlying technique (sliding window, two-pointer, BFS, memoized recursion, etc.) within 60-90 seconds of reading. Strong candidates verbalize their hypothesis out loud before coding, then iterate based on feedback. Weak candidates dive into implementation immediately, lose time on the wrong approach, and run out of time for follow-ups.
Companies update their question pools every 2-4 months. The exact wording of any given question may have been retired by the time you interview. Focus your prep on the pattern, not the specific problem. The patterns that appear in Forward Networks reports consistently are the ones worth investing in; one-off niche problems are not.
During Your Forward Networks Round
Apply the standard interview round template: clarify requirements (2-3 minutes), state your approach out loud and confirm direction with the interviewer (3-5 minutes), code with narration (15-25 minutes), test with concrete examples including edge cases (5 minutes), discuss optimization or trade-offs if time permits (5 minutes). This template is universally accepted across FAANG and adjacent companies; deviating from it produces weaker interviewer feedback signal.
The single most predictive failure mode in Forward Networks reports tagged "no hire": not asking clarifying questions. Interviewers are explicitly trained to weight this. Strong candidates ask 3-5 clarifying questions even on problems that look obvious; weak candidates dive into code immediately. The clarifying-question check is often the first signal recorded in the interviewer's written notes.