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Windows 2008 NLB, dual-nics and routing

January 30, 2009

I set up NLB in unicast mode on a couple Windows 2008 servers using dual-nics. Everything worked fine, except hosts outside the subnet could not access the cluster IP. The same setup works with Windows 2003. This is only a problem because I prefer to disable all services on the clustered NICs except IP, since I’m only load-balancing a few IP services and I want internal communication to use the primary NICs. Here’s my setup:

Server 1
-------------------------
NIC1 (Public)
IP 192.168.1.10
Gateway 192.168.1.1

NIC2 (NLB)
IP 192.168.1.11
No Gateway, File & Print, MS Client or DNS Registration

Server 2
-------------------------
NIC1 (Public)
IP 192.168.1.12
Gateway 192.168.1.1

NIC2 (NLB)
IP 192.168.1.13
No Gateway, File & Print, MS Client or DNS Registration

Cluster
-------------------------
IP 192.168.1.14

For 2008, it can be fixed with the netsh command. To get it working:

C:>netsh interface show int

Admin State    State          Type             Interface Name
-------------------------------------------------------------------------
Enabled        Connected      Dedicated        NLB
Enabled        Connected      Dedicated        Public

Note the name of the NIC used for the cluster. My case, NLB. Then run:

C:>netsh interface ipv4 set interface "NLB" forwarding=enabled

Ok.

You probably also want to make sure outbound traffic gets sent out the non-NLB interface. Otherwise, you may not get the return traffic if it gets sent to the other node. To do this, set the Metric for the Interface and the Gateway manually to a lower number on the non-NLB interface, and set the same metrics to a higher value on the NLB interfaces.
On a side note, Unicast doesn’t work inside of VMware. Use Multicast.

Filed under: Microsoft, Windows |

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