For anyone who operates with selective federation rather than an open federation model in Lync 2013/Skype for Business server, I’m sure at some point you’ve had problems when trying to setup a federation link between your platform and another SIP domain setup.
Recently, we’ve had a few customers try to federate with a new SIP domain, but when testing with them following the appropriate server-side configuration they have no luck.
What we’ve noticed is that as a rule of thumb they have been using the sip.domain.com as the access edge FQDN within the Skype control panel, however when their platform is not hosted on premises this won’t be the case.
A way to determine exactly what configuration is required you can run the below command
nslookup -q=SRV _sipfederationtls._tcp.domain.com (Change Domain to match the SIP Domain you want to federate with)
This will return the address in which the customer/partners federation _sipfederationtls._tcp.domain.com record is pointing too and in recent cases we’ve noticed that in fact they point to sipfed.online.lync.com as their infrastructure is hosted by Microsoft.
So, all that is required is the below when adding a new allowed federated SIP domain – as usual specify the domain you want to federate with but specify the Skype online access edge FQDN:
Hope this Helps