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Changing subnet mask of CAS Array / Network load balancing

Posted on 2012-08-23
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Last Modified: 2012-09-03
Hi,

We have run out of IP addresses in our current 192.168.1.x /24 network so we are changing the subnet mask to /23 in order to increase our available IPs.

We have changed this on our firewall and all servers and it's worked well but the next step is the CAS array / Network Load Balancing cluster. At present we have 2 x CAS servers in the CAS Array and in the Network Load Balancing Manager. We have changed the subnet of the actual CAS servers to 255.255.254.0 but this has not automatically changed on the NLB cluster. Within the NLB manager, I can see that I can edit the subnet on the hosts as well as the cluster itself?

Of course I will do these changes out of hours in case the whole thing crashes but is there a best practice to do the changes ie. do the hosts first, then the cluster or vice versa.

Any help would be appreciated. Thanks.
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Question by:southwestsixteen
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TI2Heaven earned 2000 total points
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The best practice its to do host first, because host ip is the primary ip. You may not need to change de mask on the mask on the nlb because the nlb ip will not be used to send traffic (only to receive).
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by:southwestsixteen
ID: 38324925
Thanks T12Heaven. How we discovered this would be an issue is because OUtlook on PCs on the 192.168.0.x range would not connect to the CAS Array so the cluster is probably not responding to them as it does not see the other range.
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by:TI2Heaven
ID: 38325456
Subnet mask is used when you send a message (request or response).
When you send a message to an nlb, both hosts will receive the message, but based on the clients IP one node will ignore the message and the other will use the MAC associated with the primary IP (this one should not be shared with the other node). Just because of that probably you will use primary ip subnet mask to route responses, and everything will function without changing nlb subnet mask, but I wouldn’t take the risk to have inconsistent data on the server and if nlb mask does not automatically change, I will changed just after both host mask has the new one.  During nlb installation, Microsoft asks to set first primary host ips and then nlb ip.
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by:southwestsixteen
ID: 38325466
Cheers. Going to try this tonight.
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by:TI2Heaven
ID: 38349618
Worked everything well?
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by:southwestsixteen
ID: 38360407
Hi T12Heaven, sorry for the late reply but we finally arranged some downtime to do this over the weekend. Yes, it all went well. I followed your advice but interestingly enough, if you change the NLB mask it asks you whether you want to change the host mask too so I guess it doesn't matter which you change first.
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by:TI2Heaven
ID: 38360424
Thank you for your feedback and your grade...
Nice to hear from you everything worked well!
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