Core Routing, Switching, and SD-WAN
This area validates your foundation for building reliable, scalable networks. Interviewers will explore how you design L2/L3 domains, implement routing policies, and ensure stability and convergence across LAN and WAN—including SD-WAN overlays and underlays.
Be ready to go over:
- L2/L3 fundamentals: VLANs, STP/RSTP/MST, OSPF areas and LSAs, BGP attributes and path selection
- Data plane vs. control plane: ECMP, CEF, fast reroute, convergence tuning
- SD-WAN concepts: Control/data plane separation, policy-based routing, DIA vs. backhaul, QoS strategies
- Advanced concepts (less common): Route reflectors and confederations, BGP communities for traffic engineering, MPLS/segment routing, underlay/overlay telemetry
Example questions or scenarios:
- “Design a WAN for 200 branches with dual ISPs and SaaS breakouts. How do you handle routing, QoS, and security at scale?”
- “Your BGP peering flaps intermittently. Walk us through your troubleshooting approach and the telemetry you’d inspect.”
- “Given asymmetric paths post-SD-WAN migration, how would you detect and remediate?”
Data Center and Cloud Networking
You’ll be assessed on fabric design (VXLAN/EVPN), Cisco ACI patterns, and how cloud networking integrates with on-prem. Expect to reason about multi-tenant segmentation, north-south vs. east-west flows, and hybrid connectivity.
Be ready to go over:
- VXLAN/EVPN: Anycast gateways, route types (2/5), L2/L3 VNI mapping, multi-site considerations
- Cisco ACI: Tenants/VRFs/BDs/EPGs, contracts/filters, L3Out patterns, brownfield migration strategies
- Cloud constructs: AWS VPC/VGW/TGW, Azure VNet/Hub-Spoke, overlapping CIDRs, DNS, hybrid routing
- Advanced concepts (less common): Multi-cloud transit, appliance insertion, EVPN DCI designs, inter-tenant service stitching
Example questions or scenarios:
- “Sketch a multi-tenant EVPN fabric with shared services and explain route leaking.”
- “Plan an ACI migration from classic 3-tier. What are your phases, risks, and rollback?”
- “Connect AWS and Azure to the DC with consistent segmentation—what’s your design?”
Network Security and Zero Trust
Security is integral, not an afterthought. You’ll discuss segmentation, identity-based access, and controls across edge, DC, and cloud. Be prepared to tie design choices to risk reduction and compliance.
Be ready to go over:
- Segmentation: Macro vs. microsegmentation, policy models in ACI, cloud SGs/NSGs
- Access control: 802.1X/MAB, Cisco ISE policies, posture assessment, guest/BYOD
- Edge and SASE: Firewall placement, SSL inspection tradeoffs, SSE/SASE integration with SD-WAN
- Advanced concepts (less common): PKI pitfalls, east-west inspection at scale, zero trust maturity roadmaps, identity-aware proxies
Example questions or scenarios:
- “Implement identity-based access on campus with ISE—what policies and exceptions do you define?”
- “Your firewall change increases latency for a payment app—how do you triage and fix?”
- “Propose a zero-trust approach for a hybrid workforce with SaaS-first usage.”
Automation, Observability, and Change Safety
AHEAD engineers reduce toil and risk with automation and rigorous observability. Interviewers will look for practical experience automating configs and tests, and building feedback loops that protect availability.
Be ready to go over:
- Automation tools: Ansible, Python, Terraform for network resources, source control workflows
- Testing and CI/CD: Pre/post checks, idempotency, linting, golden configs, canary rollouts
- Observability: Streaming telemetry, model-driven metrics, NetFlow/IPFIX, packet capture strategies
- Advanced concepts (less common): Event-driven automation, digital twins, intent-based networking, ChatOps for NOC workflows
Example questions or scenarios:
- “Automate VLAN/VRF provisioning across sites—outline your playbooks, secrets, and rollback.”
- “What signals and SLOs do you track to detect brownouts before users call?”
- “Design a pipeline to verify and deploy SD-WAN policy changes safely.”
Client Consulting, Architecture, and Delivery Excellence
Beyond engineering, you must translate business goals into architectures and guide clients through change. Expect questions on scoping, risk management, documentation, and stakeholder alignment.
Be ready to go over:
- Discovery to design: Requirements mapping, constraints, assumptions, success criteria
- Delivery mechanics: Cutover planning, MOPs, backout, hypercare, KT to ops
- Communication: Executive summaries vs. runbook detail, status transparency
- Advanced concepts (less common): TCO/ROI analyses, licensing and SmartNet planning, EA implications for architecture choices
Example questions or scenarios:
- “A client needs to reduce MPLS costs by 40% without impacting ERP. What’s your plan?”
- “Walk us through a high-risk cutover you led. How did you de-risk and communicate?”
- “How do you handle a stakeholder pushing for a design you believe is unsafe?”