Senior Network Engineer in Harlow

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 services.
• Define and deliver end-to-end wireless migration strategies, including planning, staging, cutover execution, and post-implementation optimisation.
• Architect and implement high-availability 9800 WLC deployments (SSO, redundancy models), ensuring minimal service disruption and operational resilience.
• Design and implement enterprise wireless solutions, including SSID segmentation, policy profiles, VLAN mapping, RF optimisation, and seamless roaming.
• Own the design, upgrade, and lifecycle management of Cisco ISE environments, including version upgrades, patching strategies, backup/restore, and HA topology improvements.
• Optimise ISE policy frameworks, including authentication and authorisation policies, profiling, posture, and identity-based access control.
• Design and enhance secure network access solutions leveraging 802.1X and MAB across both wired and wireless environments.
• Drive performance improvements and service optimisation across wireless and AAA infrastructure, identifying bottlenecks and implementing streamlined, scalable solutions.
• Troubleshoot 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 standards.
• Manage and escalate issues to vendors (e.g. Cisco TAC) where required.
• Produce clear and accurate technical documentation, runbooks, and support artefacts.

Job Requirements:

• Security clearance (SC cleared or the ability to become SC cleared).
• Strong understanding of TCP/IP and OSI model fundamentals.
• Experience with VLANs, trunking, inter-VLAN routing, DHCP, DNS, NTP, BGP, OSPF, EIGRP.
• Solid grounding in network security (AAA, segmentation, firewall troubleshooting).
• Ability to perform packet-level troubleshooting.
• Strong experience deploying and supporting Cisco ISE in enterprise environments.
• Expertise in 802.1X (wired and wireless), MAB, RADIUS authentication flows, and policy enforcement.
• Deep understanding of CAPWAP, AP join process, and mobility/roaming in Cisco Catalyst 9800 (IOS-XE) WLCs.
• Experience with RF design (RRM, DCA, channel/power tuning), high-density wireless environments, FlexConnect and local mode deployments.
• Strong knowledge of WPA2/WPA3 Enterprise and integration with ISE (802.1X, MAB, role-based access).

Desirable Skills:

• Experience with Cisco DNA Center.
• Experience with ForcePoint Firewalls.
• Suitable business and/or technical leadership skills in technology consulting.
• Basic automation or API exposure (ISE/IOS-XE REST APIs).
• Relevant certifications such as CCNP Enterprise, CCNP Security, Cisco ISE Specialist, CWNA/CWNP.

Soft Skills:

• Ability to diagnose cross-platform issues between ISE, WLC, and switching infrastructure.
• Strong incident troubleshooting under pressure.
• Clear and structured documentation of configurations, policies, and workflows.
• Experience working within change and release management processes.
• Effective stakeholder communication.
• Experience with vendor escalation and TAC case management.