RIP Version 2 Does Not Advertise Subnet Routes

Your Windows NT servers that are running the Routing and Remote Access Service (RRAS) Update are not advertising subnet routes for your IP networks. Instead, they are advertising one network route that summarizes the missing subnets.

The Windows NT routers are using a feature known as subnet hiding.

To resolve this problem, obtain the latest service pack for Windows NT 4.0. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

Microsoft has confirmed that this is a problem in the Microsoft products that are listed at the beginning of this article. This problem was first corrected in Windows NT version 4.0 Service Pack 5.

The feature described above, subnet hiding, is expected behavior with RIP version 1. RIP version 1 does not have a field for the subnet mask of a network and does not support subnet advertisements. When advertising routes to an external network that could not possibly know the subnet mask, the subnetted routes are reduced to a single network route or a Summary Route.

RIP version 2 is capable of advertising subnet masks; however, RIP version 2 may not advertise specific subnet routes when RIP version 1 routers could mistake the routes as host routes. This would be the case if the RIP version 1 router had a different network ID than the RIP version 2 router.

This behavior of subnet hiding is always done with RIP version 1 and is usually done with RIP version 2. With some implementations of RIP version 2, subnet hiding can be enabled or disabled.

If the announce mode is set to RIP1 or RIPv2 broadcast the subnet summarization (hiding) is always performed. You must choose RIPv2 multicast mode to disable subnet summarization.

Also, the RRAS command-line utility can be used to turn this feature on or off. The following syntax example is provided: