Senior Network Engineer

inside IR35Harlow, England Contract Our client, a prominent player in the Defence & Security sector, is seeking a Security Cleared Senior Network Engineer on a contract basis to support the delivery and optimisation of Cisco ISE (Identity Services Engine) and enterprise wireless (Catalyst 9800) platforms. This hands-on role focuses on engineering, troubleshooting, and implementation, particularly across secure network access (802.1X), policy enforcement, and wireless integration. You will play a key role in resolving complex issues, supporting upgrades, and ensuring stable, secure operation of critical network services.Key Responsibilities:Lead the design, build, and replacement of legacy Cisco Wireless infrastructure with modern Cisco Catalyst 9800 WLC architecture, ensuring scalable, resilient, and high-performance wireless servicesDefine and deliver end-to-end wireless migration strategies, including planning, staging, cutover execution, and post-implementation optimisationArchitect and implement high-availability 9800 WLC deployments (SSO, redundancy models), ensuring minimal service disruption and operational resilienceDesign and implement enterprise wireless solutions, including SSID segmentation, policy profiles, VLAN mapping, RF optimisation, and seamless roamingOwn the design, upgrade, and lifecycle management of Cisco ISE environments, including version upgrades, patching strategies, backup/restore, and HA topology improvementsOptimise ISE policy frameworks, including authentication and authorisation policies, profiling, posture, and identity-based access controlDesign and enhance secure network access solutions leveraging 802.1X and MAB across both wired and wireless environmentsDrive performance improvements and service optimisation across wireless and AAA infrastructure, identifying bottlenecks and implementing streamlined, scalable solutionsTroubleshoot complex authentication and connectivity issues, utilising packet capture and deep protocol analysis (Wireshark, TCPdump)Support change and release activities, ensuring adherence to governance and documentation standardsManage and escalate issues to vendors (e.g. Cisco TAC) where requiredProduce clear and accurate technical documentation, runbooks, and support artefactsJob Requirements:Security clearance (SC cleared or the ability to become SC cleared)Strong understanding of TCP/IP and OSI model fundamentalsExperience with VLANs, trunking, inter-VLAN routing, DHCP, DNS, NTP, BGP, OSPF, EIGRPSolid grounding in network security (AAA, segmentation, firewall troubleshooting)Ability to perform packet-level troubleshootingStrong experience deploying and supporting Cisco ISE in enterprise environmentsExpertise in 802.1X (wired and wireless), MAB, RADIUS authentication flows, and policy enforcementDeep understanding of CAPWAP, AP join process, and mobility/roaming in Cisco Catalyst 9800 (IOS-XE) WLCsExperience with RF design (RRM, DCA, channel/power tuning), high-density wireless environments, FlexConnect and local mode deploymentsStrong knowledge of WPA2/WPA3 Enterprise and integration with ISE (802.1X, MAB, role-based access)Desirable Skills:Experience with Cisco DNA CenterExperience with ForcePoint FirewallsSuitable business and/or technical leadership skills in technology consultingBasic automation or API exposure (ISE/IOS-XE REST APIs)Relevant certifications such as CCNP Enterprise, CCNP Security, Cisco ISE Specialist, CWNA/CWNPSoft Skills:Ability to diagnose cross-platform issues between ISE, WLC, and switching infrastructureStrong incident troubleshooting under pressureClear and structured documentation of configurations, policies, and workflowsExperience working within change and release management processesEffective stakeholder communicationExperience with vendor escalation and TAC case management