Environment:
Skype for Business Server 2015 – On Premise
Skype for Business Online
Issue:
In a deployment, we have setup a Skype for Business Server 2015 on premise along with an Edge pool. We have federation enabled with open federation turned off, a requirement was to federate with a client that has Skype for Business Online.
So we setup a hosted provider to Skype for Business Online using the command below:
New-CSHostingProvider –identity ‘Skype For Business Online’ –ProxyFqdn sipfed.online.lync.com -VerificationLevel UseSourceVerification –Enabled $True
We then added the domain under federated partner, and waited about 10-15 minutes for replication to occur.
I tried to search for my user account Habib@domain.com and it started to search
Then changed to Presence Unknown 
Resolution:
I began a trace and found that the error: Unable to resolve DNS SRV : Domain = domain.com
I connected to the Edge server to verify if the Edge server can perform an NSLookup and resolve the name of the server and it wasn’t able to.
I checked the network cards to validate if the DNS servers were setup on the correct NIC , it was configured on the external DMZ and not the Internal DMZ. So I then removed them from the External DMZ NIC and put them on the Internal DMZ NIC and rebooted the Edge Server. 
Once the Edge Server came backup I then tried to search for my account and the presence showed up right away.
