We have exchange 2010 in abc.com forest and exchange 2013 in zxy.com forest with Shared Name contoso.com , migration from 2010 to 2013 is flawless and everything is working fine.Because we did not do federation as we use same smtp address we went with example from http://www.expta.com/2013/08/how-to-share-freebusy-information.html which works to some extend. When I say that : It works one direction but not the other, and then in middle of the day it switches sides. I was able to see Free/ Busy calendar only once that was working on both sides fine. I am suspecting its a DNS issue however it could be something else? Can you point me out to some troubleshooting steps or what can cause some behaviour like that.
So yesterday abc.com users were able to see Free /Busy from zxy.com (GalSync in place) and today zxy.com see abc.com but not the other way around. Not sure what error logs to look into as there is probably like 20 places to look for in exchange 2013 :)
So we ran both ways
Get-ClientAccessServer | Add-AdPermission -AccessRights ExtendedRight -ExtendedRights "ms-exch-epi-token-serialization" -User "sourcedomain\Exchange Servers"
Add-AvailabilityAddressSpace -ForestNametargetdomain.com -AccessMethod PerUserFB -UseServiceAccount $true
Export-AutodiscoverConfig -TargetForestDomainControllerdc.remotedomain.com -TargetForestCredential $Target -MultipleExchangeDeployments $true
Thank you for your help.