Microsoft KB Archive/281579

= Issues with using supernetted IP address ranges =

Article ID: 281579

Article Last Modified on 7/23/2007

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APPLIES TO


 * Microsoft Windows NT Server 4.0, Terminal Server Edition
 * Microsoft Windows 2000 Server
 * Microsoft Windows 2000 Advanced Server
 * Microsoft Windows 2000 Professional Edition
 * Microsoft Windows NT Workstation 4.0 Developer Edition
 * Microsoft Windows NT Server 4.0 Standard Edition
 * Microsoft Windows Server 2003, Standard Edition (32-bit x86)
 * Microsoft Windows XP Home Edition

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This article was previously published under Q281579



SYMPTOMS
When a client is issued an. . .255 address, either from a DHCP server or by statically configuring it, the client may not be able to communicate by using the TCP/IP protocol.



CAUSE
The address is viewed as a &quot;broadcast address&quot; instead of a host address on the network. You cannot use the .x. .255 address as a client address even though it may be a valid host address.



RESOLUTION
If you are statically configuring the client's IP address, use another address. If this address is being issued by the DHCP server, exclude this address from the DHCP server's scope.



STATUS
Microsoft has confirmed that this is a problem in the Microsoft products that are listed at the beginning of this article.



MORE INFORMATION
This problem occurs when using supernetted IP addresses. Although in supernetted environments IP addresses like

. . .255 for class C based addresses

. .255.255 for class B based addresses and

.255.255.255 for class A based addresses may be valid, these are disallowed.

For example, assume the Network Address 200.57.8.0 with a netmask of 255.255.252.0, which results in a supernetted class C address range. This means for two addresses to be on the same network, the first two octets must match exactly, the first six bits of the third octet must match (252=11111100) and the last octet does not matter. For this range, 200.57.8.0 is the network address and 200.57.11.255 is the subnet broadcast address. Every IP address between those two are valid. But the addresses below are disallowed because they are subnet broadcast addresses based on the standard class C subnet mask 255.255.255.0:

200.57.8.255

200.57.9.255

200.57.10.255

Additional query words: vlsm cidr rfc1878

Keywords: kbnetwork kbprb KB281579

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