Apple Macs not communicating with Active Directory

I am writing to you asking for help and advice on a problem we are experiencing since returning from the Christmas break involving our Apple MACs which we have been using since summer 2012.

In our school, I administer 1 Mac-mini, 15 apple MacBooks & 2 iMacs, all over 5 & half years old (and in great nick). I also look after 90 iPads, well looked after via MDM. Not to forget Windows PCs & laptops.

The Apple Macs have had no problems connecting to Active Directory for users to log on throughout the past 5 years but since returning from the recent Christmas break, there had been some odd behaviour going on. At the logon screen on a Mac, a pop up appears saying either 'Network connection are unavailable' or 'Some network connections are available'. This will prevent any user logging on. Sometimes for a random length of time, the Mac waits until the pop up disappears clearing the way to log on. This states no/some network accounts are available meaning Active Directory cannot see those computers and the user cannot log on. Some at first refuse to connect to AD or connect after a certain time. There is evidence that Active Directory is not communicating with the Apple Macs even through both domain servers and Macs can ping each other. This is happening at random times.

Nothing was done to our Windows servers, (one running Windows Server 2012 and the other, Windows Server 2009 respectively) during the Christmas break i.e. updates or restarts. I had carried out some necessary Windows Updates and restarted the servers during the first week of this term as a first course of action regarding the issue but they have made no difference.

There was a time for about four days where things seemed to have settled with no further issues. Then on Tuesday the problem came back.

This is NOT to do with time synchronisation with the Domain controller, or DNS addressing. This is likely to be a communication issue between the Apple Macs and Active Directory going on randomly between the 2 iMacs, 12 Apple MacBook Pros and the Mac-mini I work on. Some are communicating and some are not. Pinging from one Mac to an AD server and back is fine, only Active Directory itself is not communicating.

Even unbinding and re-binding the Macs to Active Directory has made no difference. I had to re-bind a couple of devices to Active Directory with all previous Open Directory folders removed and received an a error message 'Authentication server an error while attempting the requested operation.' while its 'Getting Active Directory domain information ...'. \this has been attempted a number of times even with clock times are sychronised.

The Windows workstations and laptops are unaffected as well as the Apple iPads.

I have been working with these Macs for over 5 years and never had major problems joining Active Directory. But now I cannot put my finger on why this is happening and given the timing as we have returned from two weeks away so something's happened somewhere.

I will be very grateful if you share the information onto your technical support team and come back with some advice. This has been to most frustrating time dealing with the MACs and I am not getting any concrete answers from the forums and the wider internet.

Thanks