Question : Does Windows CIDR (properly)?

Our private network has grown over the past 6 years from 150 IP devices to more than 500.  The original network utilized addresses in the 192.168.1.x address range with a 255.255.255.0 netmask.  As the network grew we decided to adopt CIDR and started assigning addresses from the 192.168.0.x and 192.168.2.x address ranges.  All devices were changed to use a netmask of 255.255.0.0.

Last week I was looking for the cause of a network issue with a server when something caught my eye.  The server has an IP address of 192.168.1.10. with a netmask of 255.255.0.0.  The machine's IPCONFIG /all and routing table are attachments 01 and 02.

My understanding is that a device with an IP address of 192.168.1.10 and a netmask of 255.255.0.0 should use a "Network Address" of 192.168.0.0 and a "Broadcast Address" of 192.168.255.255.  As seen in attachment 02, the machine is instead using 192.168.1.0 as its network address and 192.168.1.255 as its broadcast address.  See attachment 3 from an on-line CIDR calculator.

Attachments 4 and 5 are for another Windows 2003 Server with an IP address of 192.168.0.160.

Attachment 6 is the output from IFCONFIG on one of our Linux workstations.  It knows how to properly calculate the Broadcast Address.

And, so does Vista.....  See Attachment 7.

So, back to the question asked in the subject of this message - Does Windows (XP, 2000, 2003) know how to CIDR?  I have been unable to find a way to remove/edit/replace the routing table entries for these machines.  Any tricks to share?

I would love to hear some speculation about the kinds of problems this situation could cause.  We seem to be having more than our fair share lately.

What can/should we do?
I started digging and found that all of our Windows XP, Windows 2000 Server and Windows 2003 Server machines have this issue.

Answer : Does Windows CIDR (properly)?

The author is correct.  Prior to Vista the TCP/IP stack in Windows didn't properly calculate the CIDR masks for broadcast addresses, especially if you were using the default Class C addressing to create a Class B or other CIDR network.  It was corrected in Vista, and also works properly in W2k8.