Assuming you allow all outbound traffic on your client (I recommend this excellent iptables config file rc.firewall_023.txt), you should now be able to mount the NFS share on the Redhat box.
DEBIAN:I used port numbers and config instructions at http://wiki.debian.org/?SecuringNFSFollow those instructions exactly and you'll have a NFS server configuration that uses static ports (instead of random assignements)REDHAT:1. Create the file "/etc/sysconfig/nfs" and add the following contents:STATD_PORT=32765STATD_OUTGOING_PORT=32766LOCKD_TCPPORT=32768LOCKD_UDPPORT=32768MOUNTD_PORT=327672. (Probably not necessary for most, but here for completeness) Append the following to the file "/etc/services":rquotad 32769/tcp # rpc.rquotad tcp portrquotad 32769/udp # rpc.rquotad udp port3. Restart the nfslock service:/etc/init.d/nfslock restart4. Run /usr/sbin/rpcinfo -p and make sure all the ports above have changed and match their ubuntu numbers. (/usr/bin/rpcinfo on ubuntu)5. I run firestarter on Ubuntu which is exporting my NFS share. I added the following policy rules for inbound traffic:Allow 32767 (from my client machine's IP)Allow 2049 (from my client machine's IP)Allow 111 (from my client machine's IP)