NLB Host Unreachable

Question

Hi All,
Our SharePoint 2010 environment is using Microsoft NLB to cluster its front end web servers.
Yesterday, one of our active directory domain controllers was demoted and the server rebooted, this server also acts as one of our DNS servers.  When it was rebooted, our SharePoint environment became unavailable; Users were getting prompted
with an authentication box.  Looking into it further there is a Host Unreachable error between the 2 load balancers.  After about 20mins the domain controller was promoted again, server rebooted and everything became available again.
Can anyone shed any light on why this may have occurred.  Is it simply that the load balancers lost the DNS and the ability to talk to each other.  If so why did it not use the secondary DNS server configured in windows and remain alive? 
Or does the issue lie with the domain controller being demoted?
Any help appreciated.
Cammie

Answer 1

Hi,
I am not very similar the SharePoint, but it seems is the client use the FQDN to access the SharePoint resource, but when your DC demote the DNS have some issue. Please try
to ping the NLB virtual IP to see it reachable or not.
If at any point the DNS Client service receives a negative response from a server, it removes every server on that adapter from consideration during this search. For example,
if in step 2, the first server on Alternate Adapter A gave a negative response, the DNS Client service would not send the query to any other server on the list for Alternate Adapter A.
The related KB:
DNS Processes and Interactions
http://technet.microsoft.com/en-us/library/dd197552(v=ws.10).aspx
Demoting Domain Controllers and Domains (Level 200)
http://technet.microsoft.com/en-us/library/jj574104.aspx
Hope this helps.
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