I have clients that use internal, but they do it as a subdomain; so internal.contoso.com

Any internal only domains that I set up are probably going to go the same way. I've used domain.local previously, and the DNS headache I get from that is immeasurable.

With so many things going "to the cloud" or whatever, the internal.domain.tld convention tends to make more sense to me.

What's everyone else doing?