how can I turn on and off the anonymous-post permission after I create a forum?

I think I can decide whether or not an anonymous post is allowed in my forum when I create it, but how can I turn it off (or turn it on) later? There looks no options to change it after a forum is created.

Any thoughts?

[originally posted on jforum.net by eiji]

Forum permissions are actually handled via group permissions. The options offered during the forum creation are for convenience and actually feed back into the groups. So, to turn off anonymous posting at a forum level you need to set up the group rights the way you want them.
[originally posted on jforum.net by monroe]