I have a current LAN network with 20+ VVX 411 desktop phones working fine.

We are trying to change to a new circuit with more bandwidth, in testing that new connection, the IP phones will not function properly.

Can someone tell me, definitively, what network address or resource these phones need to be able to communicate with to function properly? Like a URL or IP Address?

We are trying to configure routing on the new circuit to allow for the connectivity to work... and I am uncertain of what that is?

After looking in the phone settings on a phone on the working network, my guess is:

sip.ringcentral.com (199.255.120.146) , but I really need to be able to answer this question with confidence to avoiding a lot of time on the part of my network team and our internet service vendor.