Network Engineer

Ryan Mahoney

Why this role is hard · Ryan Mahoney

At this level, success has less to do with memorizing routing tables and more to do with knowing when to step outside standard procedures and explain why. During a whiteboard exercise, look for candidates who map out system dependencies instead of just following whatever the vendor recommends. Their real-world work shows up in clean change logs that spell out exact rollback triggers and honest post-incident write-ups. The best engineers sketch clear diagrams, openly point out what they might have missed, and prove they tested a change before pushing it live.

Core Evaluation

Critical questions for this role

The competency and attitude questions below are where the hiring decision is made. They run in the live interview rounds and are calibrated to the level selected above.

17 Competency Questions

1 of 17

  1. Discipline

    Network Architecture & Systems Design

  2. Job requirement

    Core Routing & Topology Design

    Independently designs and deploys scalable LAN/WAN topologies, optimizing traffic flow for transit facilities and control centers.

  3. Expected at Mid

    Mid-level engineers must independently handle normal role-scope topology deployments and traffic optimization without senior oversight.

Interview round: Hiring Manager Technical Deep Dive

Walk me through a recent multi-site network redesign or implementation you led. What steps did you take to plan and execute the transition?

Positive indicators

  • Mentions specific routing protocols and design trade-offs
  • Describes a clear staging or lab testing phase
  • Provides measurable post-cutover performance metrics
  • Highlights coordination with other teams during deployment
  • References explicit rollback or contingency planning

Negative indicators

  • Focuses only on hardware installation without routing logic
  • Describes unplanned or disruptive cutovers
  • Lacks any mention of baseline or validation steps
  • Relies entirely on vendor guidance without independent design input
  • Cannot explain why specific topological choices were made

11 Attitude Questions

1 of 11

Adaptive Automation Stewardship

The disciplined practice of managing and evolving network automation, infrastructure-as-code, and CI/CD deployment pipelines to balance rapid delivery velocity with rigorous system stability and compliance standards. It involves proactively embedding validation gates, automated rollback mechanisms, and risk-aware testing into automated workflows while continuously adapting scripts and orchestration logic based on empirical performance data and emerging operational threats. This stewardship ensures that automation accelerates reliable network operations rather than introducing uncontrolled change velocity or compounding systemic vulnerabilities.

Interview round: Peer Technical & Operational Simulation

Walk me through an infrastructure-as-code pipeline or automation script you developed for network configuration. How did you build in validation, compliance gates, and rollback mechanisms?

Positive indicators

  • References specific version control practices for automation code
  • Describes structured pre-flight validation and compliance gate implementation
  • Demonstrates rollback strategy design for automated configuration deployments
  • Provides measurable outcomes on manual effort reduction and stability maintenance

Negative indicators

  • Deploys automation without version control or rollback capabilities
  • Lacks pre-flight validation or compliance checking mechanisms
  • Cannot articulate how automation reduces risk while improving efficiency
  • Relies on manual intervention to correct automation failures post-deployment

Supporting Evaluation

How candidates earn the selection conversation

The goal is to reduce effort for everyone by collecting more useful signal before adding more interviews. Lightweight application prompts and structured screens help the panel focus live time on the candidates most likely to succeed.

Stage 1 · Application

Filter at the door

Runs the moment a candidate hits Submit. Disqualifying answers end the application; everything else is captured for review.

Knock-out Questions

1 of 2

Application Screen: Knock-out

Do you have at least 3 years of hands-on experience configuring BGP peering and implementing MACsec encryption in mission-critical or transit network environments?

Yes
Qualifies
No
Auto-decline

Video-Response Questions

1 of 2

Application Screen: Video Response

Describe explaining a complex network trade-off to non-technical stakeholders pushing for a faster timeline. How did you align on risks and a feasible path?

Candidate experience

REC
0:42 / 2:00
1Record
2Review
3Submit

Response time

2 min

Format

Recorded video

Stage 2 · Resume Screening

Read the resume against fixed criteria

Reviewers score every application that clears the door against the same criteria. Stronger reviews advance to live interviews; weaker ones are archived without further screening.

Resume Review Criteria

8 criteria
Evaluates design and deployment of VLAN segmentation and routing policies to isolate IT, OT, AFC, and surveillance traffic across multiple depot or station environments.
Evaluates configuration of BGP routing, QoS policies, or MACsec encryption to prioritize critical dispatch traffic and secure trackside fiber links.
Evaluates leadership in troubleshooting latency spikes or routing loops, coordination with dispatch/field teams, and documentation of root causes.
Evaluates development of scripts for mass device configuration, API gateway tuning, and automation of routine network deployments.

Does the cover letter or personal statement convey clear relevance and familiarity with the job?

Does the resume indicate required academic credentials, relevant certifications, or necessary training?

Is the resume complete, well-organized, and free from formatting, spelling, and grammar mistakes?

Does the resume show relevant prior work experience?

Stage 3 · During Interviews

Where the hire is decided

Interview rounds use the competency and attitude questions outlined above, then add tests, work simulations, and presentations that reveal deeper evidence about how the candidate thinks and works.

Presentation Prompt

Walk us through your approach to implementing MACsec encryption for trackside fiber backhaul links. Discuss how you would select appropriate protocols and vendors within approved architectural guidelines, manage key rotation schedules, and coordinate with field maintenance crews to minimize operational disruption.

Format

approach-walkthrough · 20 min · ~2 hr prep

Audience

Senior network architects and security compliance lead

What to prepare

  • Notes outlining your technical approach, vendor evaluation criteria, and rollout strategy
  • Optional: A high-level architecture diagram or deployment timeline

Deliverables

  • A 15-20 minute verbal walkthrough of your implementation strategy
  • Discussion of tradeoffs between security compliance and operational constraints

Ground rules

  • Focus on your reasoning and approach rather than delivering a finished design document
  • Use anonymized or hypothetical examples if your prior work contains proprietary configurations

Scoring anchors

Exceeds
Integrates security, operational, and vendor constraints seamlessly, demonstrating proactive risk mitigation and clear cross-functional alignment.
Meets
Provides a structured implementation plan that respects security guidelines and acknowledges operational constraints.
Below
Overlooks field constraints, proposes out-of-scope vendor choices, or cannot articulate a coordinated rollout strategy.

Response time

20 min

Positive indicators

  • Surfaces assumptions about field constraints and maintenance windows early
  • Balances strict security requirements with real-world operational tolerances
  • Demonstrates clear rationale for vendor/protocol selection aligned to guidelines

Negative indicators

  • Ignores field technician constraints or maintenance window realities
  • Proposes security implementations without considering operational impact or compliance mandates
  • Fails to articulate how vendor selection aligns with approved architectural guidelines

Work Simulation Scenario

Scenario. You are a Network Engineer tasked with implementing MACsec encryption across a multi-vendor trackside fiber backhaul network that supports critical OT signaling and legacy diesel bus Wi-Fi. The project requires integrating Cisco Catalyst and Juniper Junos platforms while maintaining strict latency tolerances for dispatcher radio traffic. You have a kickoff meeting with the OT Systems Lead to align on implementation constraints and validation criteria.

Problem to solve. Design a phased MACsec implementation strategy that integrates multi-vendor platforms without disrupting OT signaling or dispatcher QoS.

Format

discovery-interview · 35 min · ~2 hr prep

Success criteria

  • Surfaces critical integration constraints between OT legacy gear and modern MACsec requirements
  • Develops a phased implementation approach that protects dispatcher QoS
  • Identifies key validation milestones and rollback triggers

What to review beforehand

  • MACsec implementation guidelines for Cisco/Juniper platforms
  • Current network topology for trackside backhaul
  • Dispatcher radio QoS policy documentation

Ground rules

  • Interview an informed partner who answers honestly but doesn't volunteer info
  • Ask high-information clarifying questions before proposing architecture
  • Focus on trade-offs, risk mitigation, and operational boundaries

Roles in scenario

OT Systems Lead (informed_partner, played by cross_functional)

Motivation. Ensure MACsec deployment does not disrupt real-time OT signaling or introduce unacceptable latency for dispatcher communications.

Constraints

  • Legacy OT switches have limited buffer capacity and cannot process additional MACsec overhead during peak signaling windows
  • Maintenance windows are strictly limited to 2-hour off-peak slots twice a month
  • Vendor support for legacy gear is end-of-life, requiring custom validation scripts

Tensions to introduce

  • Notes that dispatcher radio traffic experiences micro-bursts during shift changes, which could be exacerbated by encryption overhead
  • Reveals that previous security patches caused intermittent VLAN tagging mismatches
  • Requests a rollback plan that doesn't require manual console access to remote trackside cabinets

In-character guidance

  • Provide precise latency thresholds and OT protocol details when asked
  • Share historical deployment pain points only when prompted
  • Maintain a collaborative but cautious tone regarding OT system stability

Do not

  • Do not suggest specific configuration commands or vendor workarounds unprompted
  • Do not steer the candidate toward a preferred encryption mode or key management strategy
  • Do not resolve the integration conflict for the candidate

Scoring anchors

Exceeds
Maps cross-vendor integration risks comprehensively, designs a resilient phased rollout with automated rollback, and firmly protects OT operational windows.
Meets
Identifies key integration constraints, proposes a realistic phased approach, and maintains alignment with OT stability requirements.
Below
Ignores legacy hardware limitations, proposes disruptive deployment windows, or fails to address QoS impacts on dispatcher traffic.

Response time

35 min

Positive indicators

  • Surfaces latency and buffer constraints between legacy OT gear and MACsec overhead
  • Develops a phased validation plan with explicit rollback triggers
  • Negotiates maintenance windows that respect strict OT operational boundaries

Negative indicators

  • Assumes modern encryption can be applied without assessing legacy hardware limits
  • Overlooks dispatcher QoS impacts when designing key rotation schedules
  • Fails to establish clear scope boundaries for vendor support requests

Progression Framework

This table shows how competencies evolve across experience levels. Each cell shows competency at that level.

Network Architecture & Systems Design

4 competencies

CompetencyJuniorMidSeniorPrincipal
Core Routing & Topology Design

Configures basic routing protocols and VLAN assignments under supervision, ensuring alignment with documented topology standards.

Independently designs and deploys scalable LAN/WAN topologies, optimizing traffic flow for transit facilities and control centers.

Architects enterprise routing strategies, implements BGP/OSPF optimizations, and establishes design standards for distributed transit networks.

Defines long-term routing architecture vision, drives next-generation topology evolution, and mentors engineering teams on complex design paradigms.

Systems Integration & Interfacing

Assists in API testing, endpoint verification, and basic system connectivity checks under guidance.

Integrates third-party transit applications with core network services, troubleshooting authentication and data routing issues.

Designs scalable middleware architectures for MaaS and fare system interoperability, establishing integration patterns.

Architects enterprise integration ecosystems, drives API governance frameworks, and aligns cross-domain technology roadmaps.

Transit Network Data Standards

Validates incoming data feeds against GTFS and SIRI specifications, flagging schema deviations for review.

Implements and maintains real-time data pipelines, ensuring consistent formatting and low-latency delivery to passenger systems.

Standardizes data schemas across disparate transit systems and leads integration of open-data standards into network architecture.

Champions industry-wide data standard adoption, shapes open-data policy, and architects future-proof transit information ecosystems.

Wireless & Edge Infrastructure

Installs and tests wireless access points and edge sensors, performing basic RF signal verification.

Tunes RF coverage, manages IoT edge deployments for vehicles, and resolves common interference or handoff issues.

Designs resilient wireless backhaul architectures for mobile transit environments and integrates cellular/Wi-Fi failover mechanisms.

Pioneers integrated vehicle-to-infrastructure (V2I) communication frameworks and establishes enterprise wireless strategy.

Network Operations, Security & Automation

4 competencies

CompetencyJuniorMidSeniorPrincipal
Automation & Provisioning

Runs automated scripts for device configuration backups and validates output against baseline standards.

Develops and maintains IaC templates, automating routine network provisioning and reducing manual configuration drift.

Builds CI/CD pipelines for network deployments, implements automated rollback procedures, and standardizes configuration management.

Champions autonomous network operations, architects self-healing infrastructure, and establishes enterprise automation governance.

Incident Response & Resilience

Follows established runbooks to troubleshoot network outages, documents findings, and escalates complex issues promptly.

Leads incident resolution for localized outages, implements corrective network changes, and conducts post-incident reviews.

Designs high-availability architectures, develops disaster recovery playbooks, and establishes cross-functional incident command protocols.

Directs organizational resilience strategy, oversees enterprise disaster recovery testing, and architects fault-tolerant transit networks.

Security & Access Control

Applies baseline security policies, patches network devices, and monitors access logs for anomalies.

Implements network segmentation, configures ACLs, and manages firewall rule sets for transit control zones.

Designs zero-trust network architectures, conducts security posture audits, and automates compliance enforcement.

Establishes org-wide security frameworks, integrates threat intelligence, and directs strategic risk mitigation for transit infrastructure.

Telemetry & Capacity Planning

Monitors network dashboards, tracks basic performance metrics, and escalates alerts according to runbooks.

Analyzes telemetry data to identify bottlenecks, correlates logs with performance degradation, and plans capacity adjustments.

Implements predictive analytics and SLA-driven monitoring frameworks, optimizing bandwidth allocation for peak transit demand.

Defines enterprise observability standards, drives data-driven capacity strategy, and integrates AI-driven anomaly detection.