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yum install nfs-utils libnfsidmap
systemctl enable rpcbind systemctl enable nfs-server
systemctl start rpcbind systemctl start nfs-server systemctl start rpc-statd systemctl start nfs-idmapd
vi /etc/exports
/nfsfileshare 192.168.12.7(rw,sync,no_root_squash)
Port 111 (TCP and UDP) and 2049 (TCP and UDP) for the NFS server.
There are also ports for Cluster and client status (Port 1110 TCP for the former, and 1110 UDP for the latter) as well as a port for the NFS lock manager (Port 4045 TCP and UDP). Only you can determine which ports you need to allow depending on which services are needed cross-gateway.