Exchange 2010 and Exchange 2016 co-existance Free/Busy Issues

I have a lab environment containing Office 365, Exchange 2016 and Exchange 2010.  Free busy is not working from O365 --> 2010 or Exchange 2016 --> 2010.

The Autodiscover record points all EWS requests to Exchange 2016 Web Services Virtual Directory for the Availability Service.

The Availability Service on the Exchange 2016 server is failing to lookup requests on Exchange 2010 mailboxes.

It is also important to note, the 2016 server is the one setup in Hybrid with O365, so it is responsible for looking up all Availability requests on-premises.

After doing some research into the issue, I identified that the InternalNLBBypass URL on the Exchange 2010 server must point and resolve directly to the Exchange 2010 server.  It must not be set to $null or point to the Availability Service on Exchange 2016 (in my lab that being mail.avantlab.com.au).

Exchange 2016 Web Services Virtual Directory:

Exchange 2010 Virtual Directory:

As soon as setting the InternalNLBBypassURL to point directly at Exchange 2010, this resolved the issue.

See my lab all working:

• Arya is in Office 365
• Jon is on Exchange 2010
• Bran is on Exchange 2016

And yes, they are all Game of Thrones characters :)

I blogged this one as I could not find much information online regarding this!