Ports for a Debian NFS server ?

Hi

I have set up a Debian NFS server, but I cannot access it from a client
unless I drop the firewall. That is completely unacceptable. I need to know
which / what kind (TCP / UDP) ports to open. I know that NFS by itself is
an unsafe protocol, but I wish to minimize the security risk. The client in
this case is a lab instrument that uses *only* NFS for network
communication.

I have found links through google that are relevant to Redhat but the
configuration files' locations are very different from Debian and these
links are practically useless. Any help / info would be appreciated.

Thanks.