We have a forest with a two way trust between domain1 and domain2. Here's the FSMO roles:
Schema master dc1.domain1.local
Domain naming master dc1domain1.local
RID pool manager dc1.domain2.local
Infrastructure master dc1.domain2.local
There is one DC in domain1 (dc1.domain1.local). There are two DCs in domain2 (dc1.domain2.local and dc2.domain2.local).
When we take down DC1.domain2.local and users in domain1 try to log into servers in domain2 using their domain1 user accounts the login attempts fail. Unfortunately none of the users took a screen shot so I don't know what the exact error is. They can ping and remote to it (see login prompt), but logging in fails. I can't test it without taking down dc1.domain.local but that will kill their services they're providing. Additionally their SQL connections now fail which use NTLM authentication.
both Dc1 and Dc2 on domain2 both host DNS as well and there's no WINS running if that helps.