How to update firewall to pass NFS traffic?

I have set up the NFS Service using these instructions and it was working fine last week but today I get this error:

Root-NFS: Unable to get nfsd port number from server, using default

I restarted the NFS server like this:

sudo /etc/init.d/nfs-­kernel­-server restart

and tried repeatedly but still get the error. When I google the error I see the suggestion

update firewall to pass NFS traffic

How do I update firewall to pass NFS traffic? Or should it be some other issue since it was working fine last week?