I agree, forum would be much beter if themes are sorted better.
There is no need for subcategories. You can easily make more categorise and give them proper names like:
General Networking: Remote Administration
General Networking: IP Addressing and Routing
General Networking: Interfaces
General Networking: Virtual Private Networking
General Networking: Authentication, Authorization, Accounting and General Networking: Monitoring
General Networking: Firewall and Quality of Service
General Networking: Plug-and-Play Network Access
General Networking: System Information and Utilities
General Networking: Diagnostics Tools
General Networking: Scripting Host and Complementary Tools
General Networking: IP Telephony
General Networking: High Availability
General Networking: Application Examples
I used names of topic groups in manual just for an example.