How to contact a KDC on another realm?

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http://serverfault.com – I have to set up a samba share with authentication against AD, for a customer. The network have some weirds settings. There are 2 domains. 1 with almost everything, working with samba, with no problems. But this domain only got a handful of users. All users with a mail are on the other domain, because for some unknown reason, they needed a second realm for Microsoft Exchange. The second domain is not a true domain according to their IT guys. They said it was more of an alias of domain1. So all acive directory domain controllers are on domain 1. And i need this to work with kerberos, other (HowTos)