I'm in the middle of doing side by side migration from Lync 2010 to SfB 2015 both in the same site!
I have 2015 FE pool up and running with one user in it.
I have A record in my DNS pointing to one of my servers FE2 IP to my pool name, E.G., "SKP15.domain.local" 10.10.10.32 (FE Number 2 IP).
Here is the scenario:
User2015 - is logged in to SfB 2015 and sees "User2010" as Avalible.
User2010 - is logged in to Lync 2010 and sees "User2015" as Presence unknown.
User2015 - can send only one message to "User2010" and after the first message, it won't send any more.
User2010 - cant send a message at all to "User2015".
I have used SfB debugging tool and found the next error ID - 0x80072746.
I have checked my certificates, and they are valid.
The DNS seems alright as well.
Do you guys have any other suggestions?