DNS problem

[Merlin]

Hey group,

We have 5 sites all linked via a VPN. When we came in this morning none of
our sites could ping via the DNS name, only the IP address. We noticed on
our VPN routers that the all ports are open except the Broadcast ports?

Could someone tell me do we need broadcast on our routers for DNS to work.
If so what port do we need Open?

We have windows 2000 servers, and all the sites clients are on static IPs

Many Thanks
Merlin