NortonES2 is only half correct. Teaming is one good way to make use of dual NICs, but I have seen plenty of other occasions where having a dual-homed system makes sense. That being said, it is a bad idea to have a dual-homed domain controller because it tends to mess up DNS. Both IP addresses end up getting registered in DNS as DC resources, and the hilarity ensues.
If you absolutely must run a dual-homed DC then you need to make sure that only one of the NICs is configured to register with DNS (go into NIC propertries --> TCPIP --> DNS tab.
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