Where can I ask questions regarding
- IP subnetting
This was recently discussed on How can we improve moderation of IP networking.
In short, theoretical questions about how the protocols work should go to StackOverflow. Implementation / Configuration questions to ServerFault
Update: I suggest asking both theoretical network protocol questions and Network Engineering implementation / config questions on Network Engineering.
It's unclear what you mean by ip subnetting, but if you have an ip subnetting question, please consider the existing answers as a possible solution:
From the about link of serverFault:
Server Fault is a site for system and network administrators needing expert answers related to managing computer systems in a professional capacity.
And from about link of SuperUser:
Super User is a Q&A site for computer enthusiasts that’s free.
Just to let you know that currently, there's a new beta round of a Network Engineering Stack Exchange site. Beta means that it is temporary and will disappear unless it has a decent amount of activity with regards to questions, answers and quality of answers.
Hope that helps.