What i want is exactly that, but with some esteroids
I only want have one domain.
I don't want user from local B must have his files in local A, the sites are connect via VPN, but i don't want they always depend on that.
I want have in local B a slave server (or RODC) in the case that the logon server in local A fails, users from local A can logged on, in inverse order, i want users in local b can login even if server from local B is down.
Yes i'm ware that if the server in the local B is down, the users don't have their files, because of that problem, i do the backups over the VPN on the night.
Maybe the sites situation you refer should do the trick... but i don't see that in univention docs... so i'm searching and try what i can to do what i pretend... don't even know if i'm do it the right way or if is that possible.
If i use the site model, if server from site B is down, the users from that site can still log on using site A?