DNS Rollover

I have a cable line and a fiber connection to my small business network.  Both have static IPs.   I have my Firewall configured to route to internal servers from either connection.  I have failover configured on my firewall that if one line goes down, the other will take over.  

How does automatic failover work from a public DNS perspective?  My public DNS is hosted by Network Solutions.  I currently have each sub.domain associated with a public ip from each source.  

    sub.domain.com - (Cable)
    sub.domain.com - 444.444.444.444 (Fiber)

    sub2.domain.com - (Cable)
    sub2.domain.com - 445.445.445.445 (Fiber)

My fiber line is currently down.  Only 1/2 of my remote endpoints can find their way home. Over a few hours more found there way home but not all.   I called Network Solutions who informed me that they don't rollover from one to the other IP if one is down.    

How is this normaly handled??
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Mohammed KhawajaManager - Infrastructure:  Information TechnologyCommented:
You have keep few things in perspective and they are as per below:

1. Caching:  End user PC keep a list of cached DNS entries and after a while, DNS entries are resolved against a DNS server
2. Caching:  Some servers also keep cached information and feed it to workstations

Things only get complicated as it keeps going up the chain (i.e. client to DNS server referral to another DNS...).

It all depends on how things are setup.  Is it possible to have one of your users who cannot connect to either flush DNS cache (ipconfig /flushdns) or reboot and see what happens.

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Windows Server 2012

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