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New setup Lync 2010 (i.e. OCS 2010). I have serious problems getting my edge system going.

Internally things work fine. Externally I am stuck. I have used the tester at and it also fails.

NOTE: I use the domain / xample.local here just as example.

Here is the setup. I have 2 internal hosts (lync.xample.local, edge.xample.local). is also correctly in dns. and points to the edge.xample.local external assigned ip address (external interface).

Externally, I have the following dns entries:

  • _sip._tcp -> 443
  • _sipfederationtls._tcp -> 5061
  • _sipinternaltls._tcp -> lync.xample.local 5061
  • _sip._tls -> 443

My problem is that the ocs connection test always ends up trying to contact lync.xample.local (i.e. the internal address) when connecting to The error is:

Attempting to Resolve the host name lync.xample.local in DNS. This shows me it clearly manages to connect to SOMETHING, but it does either fall through to the _sipinternaltls._tcp entry, OR it does get that internal entry wrongly from the edge system.

  • Am I missing some entries or have some wrong?
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up vote 1 down vote accepted

If the _sipinternaltls._tcp record is resolvable, the Lync client will alway try to connect to it.

You need a 'split horizon' aka 'split brain' DNS, where you have one set of records visible internally, and one set of records visible to everyone else.

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I have nothing against it trying to connect to _sipinternaltls, AS LONG AS IT GOES ON TRYING THE EXTERNAL _sip WHEN THAT FAILS. This is what OCS did. There was simply no need for split DNS there becasue the client, failing to find the internal server, would go on to the external one. With Lync, it seems to not even try to get the external one. – TomTom Mar 7 '11 at 7:29
As annoying as it is, Froosh is right -- Lync's only supported configuration now is split-brain DNS which I admit is a nasty hack. You might be able to get away with pushing registry keys via GPO that sets manual provisioning with the right server names... I'm not sure of the feasability of that. Worth investigating if it's a showstopper. – Peter Grace May 9 '11 at 15:32

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