Aleš Križanič
Networking & Infrastructure Engineer
Networking and Linux infrastructure, end to end: I design, build and secure both — from Cisco routing, switching and firewalls to servers, virtualization and automation. Based in Slovenia, working with clients wherever the work is.
I've spent the last decade and a half moving between network engineering, network security and Linux/Unix system administration — usually all three at once, since in practice they're rarely separate problems. Most recently I worked as a Cisco TAC Security Technical Support Engineer, troubleshooting firewall platforms (ASA, FTD, FMC) for enterprise customers: routing and connectivity issues, packet captures, flow analysis, hardening and performance tuning. Before that, several years of freelance and in-house work building and running Linux server infrastructure — DNS, mail, HTTP, VPN, monitoring, GitLab — and the networking that ties it together.
I like infrastructure that's boring in the best way: predictable, documented, monitored, and hard to break by accident.
Experience
Most of my hands-on network and security work comes from two places: several years as a Cisco TAC Security Technical Support Engineer, troubleshooting ASA, FTD and FMC firewall platforms for large, mission-critical networks often spanning thousands of devices across multiple sites — routing and connectivity issues, packet captures, flow analysis, hardening and performance tuning; and, earlier, direct Cisco network administration (switches, routers, firewalls) alongside software development.
On the Linux and infrastructure side, I spent several years freelancing in Slovenia, building and running server infrastructure end to end — DNS, mail, HTTP, proxy, monitoring, GitLab, file and VPN servers — plus networking configuration that ties it together. Earlier roles added Unix administration on HP-UX and AIX, datacenter security, and Windows system and network administration for a school's IT environment.
I also come from a software development background — C++, Java, Python — that mostly shows up now as an automation habit: if I'm doing something by hand a second time, it's usually a sign it should be a script.
Skills
Networking
Design, implementation and troubleshooting for small-to-mid network environments — the kind where one person can reasonably understand the whole topology.
- Cisco routing & switching
- VLAN segmentation & VPN
- High-availability design
- Network design for small/mid infrastructure
Security
Firewall-centric security work, from day-to-day hardening to root-causing why a firewall policy isn't doing what it's supposed to.
- Cisco ASA, FTD & FMC firewall platforms
- Policy design & hardening
- Packet capture & flow analysis
- Incident troubleshooting & root-cause diagnostics
Linux & infrastructure
Server infrastructure that's documented, monitored, and doesn't depend on any one person to keep it running.
- RHEL & Debian administration
- Virtualization: Proxmox, KVM, VMware
- Core services: DNS, mail, HTTP/proxy, VPN, monitoring
- Backup & disaster-recovery practices
Automation & tooling
Scripting and tooling that make infrastructure changes repeatable instead of one-off.
- Python & Bash scripting
- Configuration management (Ansible)
- Version control & CI groundwork (Git, GitLab)
- Containerization (Docker)
How I work
- Document the setup well enough that someone else — or future me — can pick it up cold.
- Test the failure case, not just the happy path — a backup you haven't restored isn't a backup.
- Automation scripts handle the repeatable; I handle the judgment calls.
- Explain the trade-off, not just the recommendation — you should understand why, not just what.
Certifications
CCNA
Contact
- email akrizanic [at] rekex [dot] si
- linkedin linkedin.com/in/akrizanic
- location Slovenia — open to relocation
- languages Slovenian (native), German (fluent), English (fluent)