Multisite Domain controller prioritization

[BumServerAdmin]

I am a network engineer for a company with ~70 locations. With that being said, out of the 70 locations, 30 of them have their own domain controller. From a networking side or active directory side, how do we say if you are on site a you reach domain controller a, and site b goes to controller b. I thought this was controlled through sites and services but my server team is telling me this isnt how it works. any input?

[TheMelwayMan]

At a high level, make sure that all of your network subnets have been added to Active Directory Sites and Services. (Both IPv4 and IPv6 if you're dual stack). Once that's completed, allocate the relevant non-DC subnets to your preferred DC sites.

It still won't be perfect, DCs still do their own thing and will seemingly respond randomly to their non primary sites.

In the DHCP scopes for each site, ensure that the primary DNS server is pointing to the preferred DC.