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I'm configuring a website in IIS6 to restrict access to a customer's IP address range. I've been given their IP address ( and an IP range (172.17) which I am meant to allow access to.

I can see how to grant access in IIS to a single IP address, but when granting to a group of computers I am prompted for a Network ID and Subnet mask, but am unsure how to work out what these should be, based the information I have been given.

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This is on a private network, right? 172.17 is not a valid address on the public Internet, per RFC1918. – David Schwartz Jan 9 '12 at 9:44
No, they are accessing the site from their [external] network. Does this mean I have been given the wrong information? – Matthew Dresser Jan 9 '12 at 9:48
Yes, since you will never see requests from 172.17 coming over a non-private connection. (If there's a VPN or tunnel of some kind, then maybe. But not over a normal Internet connection.) – David Schwartz Jan 9 '12 at 9:56

The network is

This translates to a network ID of and a netmask of

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Does this mean I ignore the actual IP address altogether? – Matthew Dresser Jan 9 '12 at 10:10

It is possible that the question is correct but it hasn't been thought about correctly:

If there is no vpn, then you may be able to look at the firewall at the remote end if allowed and and do something there to limit access, as at your end your firewall/iis server you will only see requests from the remote end's external ip rather than the 172 addresses.

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