RIP Does Not Advertise Zero Subnets

• Microsoft Windows NT Server version 4.0
• Microsoft Routing and Remote Access Service Update for Windows NT Server version 4.0

SYMPTOMS

Your computer running both Windows NT Server and the Routing and Remote Access service are not advertising all of the correct routes to all of your networks. The subnets that are not being advertised are the subnets with a zero as the last octet in the subnet ID.

CAUSE

The Routing and Remote Access servers discard zero subnet advertisements.

RESOLUTION

Obtain the Routing & Remote Access Service Hotfix Update mentioned below.

STATUS

Microsoft has confirmed this to be a problem in Routing and Remote Access Update for Windows NT Server version 4.0. This problem was corrected in the Routing & Remote Access Service Hotfix Update. You can obtain this update from Microsoft's World Wide Web Site on the Internet at the following location:

   http://www.microsoft.com/communications/routing&ras.htm

   http://www.microsoft.com/

MORE INFORMATION

The zero subnet is easier to identify using the following example:

Consider a class B address of 172.16.0.0 that is subnetted with a 255.255.192.0 mask. The valid subnet IDs will be 172.16.0.0, 172.16.64.0, 172.16.128.0, and 172.16.192.0. For this example, 172.16.0.0 is the zero subnet ID. This zero subnet will not be advertised and, therefore, will not be reachable from other networks.

Traditionally, a zero subnet ID was considered invalid, but the practice of discarding these subnets is now obsolete. A complete discussion of this practice can be found in RFC 1878, which can be found at the following Internet location:

   http://www.internic.net