Enterprise Networking
Enterprise switching, routing, and high availability.
- VLAN, STP and LACP
- OSPF and BGP
- Redundancy and HA
Network Engineering Knowledge Base
Practical network engineering field notes.
Technical articles, configuration guides, and real troubleshooting approaches for enterprise networking, network security, Aruba Networking, ClearPass, and Fortinet.
03Articles
04How-To
04Troubleshooting
00Cheat Sheets
FOCUS AREAS
Technical areas I focus on.
Field-tested configurations, troubleshooting records, and reusable technical notes.
Network Security
Firewalling, segmentation, VPN, and secure access.
- Firewall policy design
- SSL inspection
- IPsec and access security
Aruba & ClearPass
Switching, wireless, NAC, 802.1X, and EAP-TLS.
- Aruba CX
- ClearPass Policy Manager
- Wireless and onboarding
Fortinet
FortiGate-centered security and troubleshooting.
- FortiGate
- FortiManager / FortiAnalyzer
- Web Filter and SD-WAN
IAM
Enterprise Identity & Access Management
Dynamic authorization and device-aware access control across wired and wireless networks.
01
802.1X & RADIUS Integration
Centralized authentication designs integrating Aruba ClearPass, Cisco ISE, or Microsoft NPS with Active Directory or LDAP.
02
Dynamic VLAN Assignment
Applying VLAN and access policies dynamically based on user group, device type, or certificate state.
03
PKI & Certificate Management
Enterprise CA integration and client certificate distribution for EAP-TLS authentication.
LATEST CONTENT
Read it, apply it, troubleshoot it.
Selected How-To guides, troubleshooting cases, and technical articles.
TROUBLESHOOTINGTS-005 · Solve the problem systematically
Aruba AP-314 Will Not Join an Instant Cluster: SetMeUp and Standalone Behavior After IAP Conversion
A real-world case where an Aruba AP-314 converted with an IAP image could discover the existing Instant cluster and complete config sync but still fall back to standalone SetMeUp mode, resolved by correcting conversion-related environment parameters.
PUBLISHEDRead article →
HOW-TO21 Sep 2026 · Apply it step by step
FortiGate Security Profile Design: A Department-Based Guide to Web Filter, IPS, Application Control and SSL Inspection
A practical guide to designing role-based FortiGate Security Profiles for Web Filter, Antivirus, Application Control, IPS, SSL Inspection, File Filter and DNS Filter, including profile groups, comments, staged enforcement and validation.
PUBLISHEDRead article →
ARTICLE7 Sep 2026 · Understand the concept
Aruba Controller Cluster AP Load Distribution and Failover Capacity
A practical capacity-planning guide explaining why AP count alone is not enough in Aruba Controller Cluster environments, and how client load, throughput, CPU, memory, and failover capacity should be evaluated together.
PUBLISHEDRead article →Publishing approach
Implemented or validated technical records are published with environment-specific information replaced by safe example values.
TROUBLESHOOTING LIBRARY
Real problem → systematic checks → validated result.
Cases that show how the problem was narrowed down and what each test actually proved.
TS-001
FortiGate Proxy-Based Web Filter: Why Are Specific Domains Not Being Blocked?
A real FortiGate Proxy-Based Web Filter troubleshooting case where vendor engineering confirmed invalid regular expressions in the WAD/Hyperscan regex database as the root cause of specific domains not being blocked.
Symptom
A general wildcard worked, while specific domain entries did not match as expected under Proxy-Based inspection.
Approach
Policy → profile → inspection → WAD/Hyperscan compile check → regex validation → Proxy-Based retest.
Verification
After the invalid regex entries were corrected, the target domain was successfully blocked under Proxy-Based inspection.
TS-003
Aruba Controller Cluster ISOLATED Node: Analysis and Recovery Steps
A systematic ArubaOS 8 troubleshooting and recovery approach for a controller cluster node in ISOLATED state, covering cluster membership, Config ID, configuration state, peer communication, and config/database synchronization.
Symptom
One cluster member appears as ISOLATED instead of CONNECTED or cannot maintain healthy cluster communication with its peers.
Approach
Follow cluster membership → management/config sync → peer communication → cluster state → controlled recovery.
Verification
Confirm all members return to CONNECTED, config sync succeeds, and AP/client services operate as expected.
TS-004
FortiGate SIP ALG and VoIP Troubleshooting: Why Does the Problem Continue After ALG Is Disabled?
An advanced FortiGate VoIP troubleshooting approach for one-way audio, calls dropping around 32 seconds, and REGISTER issues that continue after SIP ALG is disabled, separating session-helper behavior, NAT/SDP/RTP, packet capture, and NPU visibility.
Symptom
After FortiGate deployment or a configuration change, one-way audio, calls dropping around 32 seconds, or unexpected loss of SIP REGISTER traffic is observed.
Approach
Separate SIP signaling from RTP → identify whether FortiGate is using ALG or session-helper → review NAT/SDP and the session table → capture packets → disable NPU offload only for controlled testing if needed.
Verification
Confirm the INVITE/200 OK/ACK flow completes, REGISTER succeeds, and RTP flows in both directions using the expected addresses and ports.
ABOUT
Özgür Koca
Senior Network Architect · Bursa, Türkiye
Technical notes built from hands-on experience in enterprise networking, network security, Aruba Networking, and firewall environments.
This site organizes reusable troubleshooting methods and configuration guides into a practical knowledge base.
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