Use these two dialog boxes to list the computers, groups of computers, or domains that you want to grant or deny access to this resource.

Single computer

Click to define access rights for a single computer.

If you select a single computer you will need to know the IP address of the computer.

IP address

Type the Internet Protocol (IP) address of the computer.

DNS Lookup

Click to look up a specific computer's IP address using the domain name (for example, In the DNS Lookup dialog box, type the DNS name for the computer in the Type the DNS name box, and click OK.

You can configure IIS to perform a DNS lookup every time access is requested for the site, virtual directory, or file. However, using the DNS lookup each time a request is made can affect server performance.


If you get a "Host not found" error, either the domain name you typed in is incorrect, or the computer you referred to is not available on the network.

Groups of computers

Click to define access rights for a group of computers based on network ID and subnet mask.

When you grant or deny access to groups of computers, you are required to identify them by network ID and subnet mask. A subnet mask, or address mask, is a numerical address of a subnet that includes the network. The mask simply overlays all but the significant part of the network address. Ask your network administrator for information about TCP/IP networking, IP addressing, and the use of subnet masks.

Network ID

This identifies the numerical address of the network that the group of computers belong to.

Subnet mask

This identifies the address mask that, to make the subnet address unique, replaces all but the non-significant numbers of the network ID in order to make the subnet address unique.

Related Topics

To learn more about security and FTP authentication, see the IIS 6.0 online documentation on the Microsoft Windows Server TechCenter.