Senior Network Security Engineer; L4

Position: Senior Network Security Engineer (L4)
Location Bloomsbury Square, London, United Kingdom# Senior Network Security Engineer (L4) at N Consulting Ltd Location Bloomsbury  Square, London, United Kingdom Salary £65 - £69 /year

Job Type Full-time

Date Posted December 9th, 2025

Apply Now
** Role:
** Senior Network Security Engineer (L4)
*
* Experience:

** 10years
*
* Location:

** Guildford,UK
** Work mode:
** Onsite
* * Role Overview
** We are seeking a highly skilled L4 Network Security Engineer with deep expertise in Cisco security technologies, Check Point firewalls, and F5 APM. The ideal candidate will be responsible for designing, implementing, optimizing, and troubleshooting enterprise security solutions across multi-site and data center environments. This role requires hands-on experience in platform installations, upgrades, migrations, and decommissioning activities, along with strong troubleshooting and cross-team collaboration skills.
** Key Responsibilities
** 1. Security Infrastructure Operations & Engineering Manage, configure, and troubleshoot Cisco ISE (TACACS+, RADIUS, Dot1X, CoA, Profiling). Administer and support Cisco ASA/FTD firewalls including ACLs, NAT, VPN, failover, clustering, and upgrades. Manage Check Point firewalls (R80.x) — policy management, clustering, VPN, logging, and health checks. Handle F5 APM for remote access VPN, SSO, authentication policies, and application access. Support data center network security architecture (firewalls, segmentation, VRF, routing, switching security).2. Implementation, Installations & Decommissioning Perform installation, configuration, and deployment of security devices (ASA/FTD, Check Point, ISE nodes, F5 APM).

Lead hardware refresh, firewall replacement, and migration projects. Execute device decommissioning, ensuring proper cleanup of configs, rule removal, rack removal, and documentation. Conduct cutover activities, change execution, and post-implementation validation.
3. Project & Architecture Support Participate in designing secure network architectures for enterprise and data center environments. Work with cross-functional teams to review network and security requirements. Create and maintain HLDs/LLDs, network diagrams, migration plans, and SOPs.
4. Security Operations & Troubleshooting Act as L4 SME for escalations related to network security issues. Troubleshoot identity/authentication failures, VPN issues, firewall packet drops, routing conflicts. Perform root-cause analysis (RCA), remediation plans, and long-term fixes. Monitor system health, logs, and alerts across multiple platforms.
5. Governance, Compliance & Best Practices Ensure compliance with security standards (ISO 27001, NIST, PCI-DSS, CIS benchmarks). Conduct periodic rule/policy optimization, cleanup, and audits. Maintain device firmware/software to secure and supported versions. Document operational procedures and provide knowledge transfer to L1/L2 teams.
** Required Skills & Experience
**** Technical Skills
** Cisco ISE (expert level) – Authentication policies, authorization profiles, profiling, certificates, device onboarding.

Cisco ASA/FTD – VPN, NAT, ACL, clustering, routing, packet tracer, Firepower Management Center (FMC).Check Point R80.x – Smart Console, VPN, IPS, rule optimization, HA/cluster.

F5 APM – Access policy creation, VPN configuration, SAML/OAuth integration.

Cisco Switching/Routing in DC environment – Nexus (5k/7k/9k), VLANs, VPC, OSPF/BGP basics.

Packet capture tools:
Wireshark, tcpdump.cloud networking (AWS/Azure) is a plus.

Automation/Scripting knowledge (Python, Ansible) preferred but not mandatory.
** Experience
* * 6–10+ years of strong experience in enterprise Network Security.

Experience working in large, distributed, high-availability environments.

Proven track record of leading install, upgrade, migration, and decommission projects.

Experience in handling major Incidents and RCA documentation.
** Soft Skills
** Excellent communication and documentation skills.

Strong analytical and troubleshooting capability.

Ability to lead changes independently and collaborate with global teams.

Ability to mentor junior engineers.
#J-18808-Ljbffr