How to Find the Lync/SfB Federation SIP Address of a Domain

Being the Lync / SfB Administrator of your company, you may at times need to look up the Federation SIP Address of another domain. It may happen that a federated partner domain decided to change their SIP Address or perhaps they've migrated their Lync On-Premise infrastructure to O365/Skype Online, and you need to update your own Lync organization with that new SIP Address.
Federation utilizes the SRV DNS record with a specific format, and for this, you can use the good old nslookup utility.

In this example, we are looking for the Federation SIP Address for microsoft.com. The result is sipfed,microsoft.com

C:\>nslookup
> set q=srv
> _sipfederationtls._tcp.microsoft.com
DNS request timed out.
    timeout was 2 seconds.
Non-authoritative answer:
_sipfederationtls._tcp.microsoft.com    SRV service location:
          priority       = 0
          weight         = 0
          port           = 5061
          svr hostname   = sipfed.microsoft.com
>

Looking at the example, the federation sip address always starts with _sipfederationtls._tcp. and followed by the actual domain.

eg.
_sipfederationtls._tcp.amazon.com
_sipfederationtls._tcp.contoso.com

References:
https://technet.microsoft.com/en-us/library/jj618369(v=ocs.15).aspx
http://windowsitpro.com/skype-business/understanding-main-types-federation-skype-and-lync-environments
https://www.petri.com/setup-lync-federation

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