Active Route gets removed on Windows Server 2008 offline Cluster IP Address

An interface on a Windows 2008R2 cluster was no longer reachable. It was a management interface, and the machine was still up, but of course the server came up in the monitoring as not reachable. There was a persistent route present on the server, but somehow this route got removed from the active routing table.

Some searching by one of my colleagues turned up this article: http://blogs.technet.com/b/networking/archive/2009/05/21/active-route-gets-removed-on-windows-server-2008-offline-cluster-ip-address.aspx

Apparently when adding persistent routes on cluster nodes you need to make sure that you specify the interface as the destination rather than the next hop IP address. An example:

Adding a route as usual, open a command prompt: route add -p 10.10.0.0 mask 255.255.0.0 10.10.10.1

This would route all traffic to 10.10.x.x addresses via 10.10.10.1, and the only interface on the host (e.g. with host IP address 10.10.10.20) within that network range would use that route. However, this route could dissapear from the active routing table *despite having a persistent route* because the next hop specified is part (or could be part) of a clustered network.

With Windows 2008 (and R2) you need to add it a little bit differently for cluster nodes, according to the Technetblog:

• Open up the Network and Sharing Center
• Click Change adapater settings
• Look at the interface you want the route for and note which the "Device Name" of the interface (see screenshot). As an example, the first interface in the screenshot is the one that needs the route. It has device name "Intel(R) PRO/1000 MT Network Connection #3"

• Open up the command prompt as administrator
• Type route print, and look at the first lines that show the interfaces:

As you see the Intel interface with #3 at the end has a number in front of it: 21 in this case. This is the Interface Number

• Now type the route you want, e.g.: route add -p 10.10.0.0 mask 255.255.0.0 0.0.0.0 if 21

The trick is to add "0.0.0.0 if <interface number>" instead of the next hop address. Now, the route will stay and you will have your connectivity regardless if a Clustered IP Address is online or offline.