Oğuzhan Semin

Senior Network & Security Engineer | FortiGate, Cisco, Arista, Checkpoint, F5, IPSec/SSL VPN | Security Hardening & Infrastructure Consultant

Istanbul, Türkiye

About

I'm a Senior Network and Security Engineer with over a decade of hands-on experience in securing, designing, and optimizing complex enterprise infrastructures. Throughout my career, I’ve taken ownership of mission-critical systems, managed high-availability network environments, and implemented advanced security solutions for large-scale organizations across finance, retail, and digital gaming sectors. 🔐 My core expertise includes: • Fortinet FortiGate firewalls (600E/600F): Policy design, HA clustering, IPS/IDS, Web Filtering, SSL/IPSec VPNs • Cisco enterprise networking: L2/L3 switching, BGP, OSPF, VLAN segmentation, STP, EtherChannel, Nexus platforms • Arista switches: Backbone design, uplink aggregation, MLAG/VLAN configuration, CLI-based management in data center environments • F5 Load Balancer: Pool creation, Virtual Server setup, iRules for advanced traffic management • Security Operations: PAM integration, vulnerability scanning, attack surface reduction, DDoS mitigation (Arbor APS) • Infrastructure monitoring: Zabbix, PRTG, Graylog log aggregation and alerting • Remote troubleshooting and secure access control for multi-site environments (MPLS/IPSec integration) 🚀 Currently, I manage and secure the entire network infrastructure of Misli.com – a high-traffic digital gaming platform. I lead firewall operations, secure hybrid environments, support DevOps and InfoSec teams, and ensure 24/7 uptime across on-prem and cloud systems. 💼 In addition to my full-time role, I provide freelance services and remote consultancy on: • Firewall implementation and rule hardening • Network redesign, segmentation, and troubleshooting • Secure VPN tunnels for remote workforce and branches • Infrastructure audits and post-incident recovery plans 🌍 I'm actively open to remote work, short-term projects, and global freelance collaborations — particularly in firewall configuration, secure networking, and enterprise-level troubleshooting. Let’s connect and discuss how I can help secure and optimize your network.

Experience

  • Senior Network Security Engineer at Misli
    Oct 2023 - Present · 2 yrs 9 mos

    Veri merkezi ve ofis network & güvenlik altyapısının yönetimi FortiGate, F5 Load Balancer, Arista Router yönetimi DDoS koruma, PAM ve network izleme süreçlerinin yürütülmesi ******************* Managing data center and office network & security infrastructure Administration of FortiGate, F5 Load Balancer, and Arista routers Responsible for DDoS protection, PAM, and network monitoring

  • Network ve Güvenlik Uzmanı at Ayaydin-Miroglio Group
    Apr 2021 - Oct 2023 · 2 yrs 7 mos

    Cisco Nexus & C9200L switch yapılandırma ve yönetimi CheckPoint ve FortiGate firewall yönetimi, IPsec VPN kurulumu Zabbix & Graylog ile loglama ve izleme süreçlerinin yürütülmesi ***************************** Managed Cisco Nexus & C9200L switch configuration and operations Administered CheckPoint and FortiGate firewalls, deployed IPsec VPN Handled log management and monitoring using Zabbix & Graylog

  • Network Administrator at Dünya Varlık Yönetim A.Ş.
    Nov 2019 - Apr 2021 · 1 yr 6 mos

    Cisco & HP switch yönetimi ve NAC entegrasyonu Cisco ASA firewall konfigürasyonu ve monitoring (PRTG) Network güvenliği ve kullanıcı erişim yönetimi ********************* Managed Cisco & HP switches and NAC integration Configured Cisco ASA firewall and monitored via PRTG Ensured network security and access management

  • Sistem Ve Network Sorumlusu at Adaş Giyim
    Feb 2019 - Oct 2019 · 9 mos

    Sunucu ve network altyapısının yönetimi İnternet devreleri ve Wi-Fi sistemlerinin izlenmesi IT altyapısında hızlı sorun giderme ve destek sağlama ************* Managed server and network infrastructure Monitored internet circuits and Wi-Fi systems Provided rapid troubleshooting and IT support

  • Network Specialist at Not Bilişim
    Apr 2018 - Sep 2018 · 6 mos

    Network cihazlarının konfigürasyonu ve uzaktan destek Firewall ve Access Point kurulum ve yönetimi Müşteri altyapılarında sorun giderme ve izleme ************** Configured network devices and provided remote support Installed and managed firewalls and access points Performed troubleshooting and monitoring for client infrastructures