[c-nsp] Problem with Microsoft NLB on Server 2008 running in Multicast mode

[Bracey, John]

Hello All:

Have any of you run into this issue?  We have an Exchange cluster running on server 2008 servers (using Microsoft NLB) that we're trying to reconfigure to use the Multicast mode of clustering that seems to be running into this issue as outlined here:

Network Load Balancing (NLB) clients cannot connect to the Windows Server 2008 NLB cluster by using the virtual IP address when NLB is running in multicast mode
http://support.microsoft.com/kb/960916

Only, in this case, the hotfix that is mentioned in the KB article has already been applied to the NLB cluster servers.

I found this document on Cisco.com that addresses issues with NLB and Server 2000/2003:

Catalyst Switches for Microsoft Network Load Balancing Configuration Example
http://www.cisco.com/en/US/products/hw/switches/ps708/products_configuration_example09186a0080a07203.shtml

but after reading this article I don't think that the Cisco documented fix will work as there have been changes to how NLB works in 2008 (according to this document):

Unable to connect to Windows Server 2008 NLB Virtual IP Address from hosts in different subnets when NLB is in Multicast Mode

http://blogs.technet.com/networking/archive/2009/01/15/unable-to-connect-to-windows-server-2008-nlb-virtual-ip-address-from-hosts-in-different-subnets-when-nlb-is-in-multicast-mode.aspx


Exerpt:
"What's the difference in Windows Server 2003 and Windows Server 2008 NLB?

The functionality of NLB is the same on Windows Server 2008 as it is on Windows Server 2003.  TCP/IP functionality has been changed in Windows Server 2008.
In Windows Server 2003, assume that we have the Virtual IP address and Dedicated Primary IP on the interface.  Whenever you try to ping the Virtual IP address from a client, the Windows Server 2003 NLB node sends out an ARP request to the Default Gateway IP address.  This ARP Request always goes from the Primary IP Address, which is a dedicated IP address with a Unicast MAC (Interface MAC) Address.
On Windows Server 2008 NLB Nodes operating in Multicast Mode, the ARP request to the Default Gateway IP Address goes from the Virtual IP Address with a Multicast MAC Address as the Sender's MAC Address and the Router (Gateway Device) never responds if the ARP request contains a Multicast MAC Address in the Sender's MAC Address field."
Our server admins have a case open with Microsoft at the moment and so far M$ tech support is telling them to have us (the Networking group) make our routers accept the mangled ARP requests from the NLB cluster servers, which I don't see how to do.

So, I see there are some workarounds out there, scheduled jobs on the NLB cluster servers to ping the gateway address every minute, static ARP entries on the NLB cluster servers, etc...

Have any of you run into this issue?  If so, were you able to help out from the Cisco side?

Thanks in advance.

*********************************************************
John K. Bracey, Sr. Network Analyst
Communications Services / Network Operations
California State University, Chico
530-898-5400
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