Issues with Using Supernetted IP Address Ranges (281579)


The information in this article applies to:

  • Microsoft Windows NT Server 4.0 Terminal Server Edition
  • Microsoft Windows 2000 Server
  • Microsoft Windows 2000 Advanced Server
  • Microsoft Windows 2000 Professional
  • Microsoft Windows NT Workstation 4.0
  • Microsoft Windows NT Server 4.0
This article was previously published under Q281579

SYMPTOMS

When a client is issued an x.x.x.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 "broadcast address" instead of a host address on the network. You cannot use the x.xx.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
x.x.x.255 for class C based addresses
x.x.255.255 for class B based addresses and
x.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
Modification Type:MinorLast Reviewed:1/25/2006
Keywords:kbnetwork kbprb KB281579
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