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NLB Strangeness

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NLB Strangeness - 19.Nov.2009 11:11:56 PM   
chrisgibbs

 

Posts: 16
Joined: 1.Apr.2009
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Hi All,

I have just investigated a strange NLB problem that I hope someone can shed some light on.

We have a production ISA cluster with 3 members. We have a number of virtual IP's for load balancing various web-farms. These 3 servers are all physical machines, 1 nic ISA setup and using NLB in unicast mode.

The problem occured when a new vmware virtual machine was deployed on the ESX environment here, completely un-related to ISA. This new mahcine when created was setup with a MAC address that was generated from the vmware pool of address space, namely 00:50:56.

As soon as the virtual mahine was powered on it came up and the ISA cluster competely stopped working. When i jumped on the server i noticed that there was a duplicate MAC address entry in the event log and that the network interface had been disabled on all three servers for a brief amount of time.

Changing the MAC address on the virtual machine was a quick work around but we really want to make sure the problem does not occur again. Checking with the IEEE MAC address allocation, the address space 00:50:56 belongs to vmware. From this i can only assume that Microsoft is assigning from the wrong space.

Now i get a little more confused since, the only record i can find of the MAC addresses for VIP's are assigned automatically.

http://support.microsoft.com/kb/556067

I did not build the cluster and cannot imagine why the previous administrator would have changed it from automatic assignment, even  if it is possible.

The strange part was that the conflicting MAC addresses were in different VLAN's and I think it was only detected since the Cisco switches do not like having the same MAC address assigned to multiple ports and vlans.......

Anyway......

Cheers

Chris

< Message edited by chrisgibbs -- 19.Nov.2009 11:15:02 PM >
Post #: 1

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