[not seeing computer on different domain controllers]

we have 6 domain controller servers under one domain

computers connected the domain controller site sync with each other no issue

But between sites the sync software does not see each other.

why?

cant be a firewall issue because the computer talk to each other at that site without any adjustment of our domain firewall.

the only issue is if PC from Site A does not see PC from Site B in the BitTorrent Sync software.

why?

how do i get these computers to talk to each other?

[not talking between subnets]

we have different sites under one domain

site ones address is 100.100.1.1

sites two address is 100.100.2.1

computers in the first site can sync with each other but if a pc from one site tries to sync with a pc in the other site inside the same domain nothing pops up.