We use a 172.24 range which has been subneted in "class C" subnets for each office. Even if I want to use a 172.24.100.0 255.255.255.0 test (ie. IP address manager...) it is refused and it ask me "" Please enter a class C only".
All my subnets have a /24 bit mask, but I can't test anyone because it's part of a 172.24.x.x network....