Folder access restriction on IIS

I need to give restriction to one of folder in my website so it can be access only from my office network.

Go to Control Panel > Administrative Tools > IIS Manager
Browse your file and choose which folder that you want to give access restriction then right click > Properties > Directory Security
Find IP address and domain name restrictions section click Edit button.
Choose Denied access and click Add...
You can choose type of restrictions you need to be allow, what i want is allow my office network so i choose Group of computers
I key in
Network ID: 10.0.0.0 (my office network ip range)
Subnet mask: 255.255.0.0