Q. I'm trying to create a trust between two forests but it's failing with remote procedure call (RPC) communication errors. What might be the problem?

A. The vital part of this process and the part that's missed most often is both domains have to be able to resolve DNS for the other forest, which essentially means you need to create a conditional forwarder in DNS for each forest that points to DNS servers for the other forest/domain. In Windows 2003 you select the Forwarders tab of a DNS servers properties (via the DNS management snap-in) and create a new DNS domain (otherdomain.com) and then enter the IP addresses of the DNS servers in the other forest. In Windows Server 2008 you create conditional forwarders in the Conditional Forwarders navigation node as shown below. Here's an example of the DNS conditional forwarding you need to configure.