Network EngineerInterview Answers

I start with requirements: number of users, applications, bandwidth needs, redundancy requirements, and security constraints. I design for the right level of redundancy — not everything needs N+2, but nothing should have a single point of failure for critical services. I produce a logical design (VLAN structure, routing design, WAN topology) before moving to physical. I document IP addressing, QoS policies, and security zones. I also plan the implementation in staged phases with rollback procedures at each step.

BGP (Border Gateway Protocol) is the routing protocol of the internet — it routes traffic between autonomous systems (ASes). In an enterprise context, I use eBGP for internet connectivity (to ISPs), SD-WAN underlay, and multi-cloud connectivity. iBGP is used to propagate routes within large enterprise networks where OSPF or EIGRP isn't practical. BGP gives precise control over path selection via attributes like AS-path, local preference, MED, and communities. It's the right choice when you need policy-based routing between autonomous systems.

I follow a structured approach: define the problem clearly (what's affected, what's not, when it started), gather data (logs, monitoring alerts, interface stats), form a hypothesis, test it without causing further disruption, implement a fix, and verify recovery. I use the OSI model as a structured framework — physical, data link, network, transport. I check spanning tree, CDP/LLDP neighbors, routing tables, and logs in sequence. I document every step during a critical outage so I have a timeline for post-mortem.

I've designed and deployed SD-WAN solutions using Cisco Viptela, VMware (VeloCloud), and Fortinet Secure SD-WAN. I've replaced MPLS with broadband + LTE underlay combinations, implementing application-aware routing policies, dynamic path selection based on SLA metrics (latency, jitter, loss), and centralised management. SD-WAN reduced WAN costs significantly while improving application performance for cloud-hosted applications. The key to a successful SD-WAN deployment is clear traffic classification and SLA policy design upfront.

I implement defence in depth: perimeter security (next-gen firewalls, DDoS mitigation), network segmentation (VLANs, micro-segmentation, zero trust zones), access control (NAC, 802.1X, device posture assessment), encrypted communications (IPSec VPN, MACsec for internal), and monitoring (NetFlow, SIEM integration, IDS/IPS). I apply least-privilege to firewall rules — deny all, permit by exception. I audit ACLs and firewall rules quarterly and conduct regular vulnerability assessments. Security is a continuous practice, not a one-time configuration.

I've designed AWS and Azure network architectures: VPC/VNet design, Transit Gateway and Virtual WAN for hub-and-spoke, Direct Connect and ExpressRoute for private connectivity, and AWS PrivateLink/Azure Private Endpoint for secure service access. I implement cloud-native security: Security Groups, NACLs, and NSGs. I use Terraform to deploy and manage cloud network infrastructure as code. I understand the shared responsibility model and ensure we're meeting our side of the security equation in every cloud deployment.

I hold [CCNP/CCIE/PCNSE/NSE4] and keep them current through CPD requirements. I follow Cisco and vendor release notes for platforms I manage, participate in vendor webinars, and use lab environments (GNS3, EVE-NG, or vendor sandboxes) to test new technologies and configurations before deploying to production. I also follow the networking community — PacketPushers, network engineering forums, and NANOG conference proceedings for emerging trends and real-world implementation discussion.

I follow a structured change management process: all changes documented with a detailed plan, rollback procedure, and test plan. I categorise changes by risk (standard, minor, major, emergency) and route accordingly through the change advisory board (CAB). Major changes are tested in a lab first. Production changes happen in defined maintenance windows with the team on a bridge, and I maintain a live timeline of changes made. Post-change testing confirms success before bridge release. I also write runbooks so changes can be executed by other team members.