How to Export an NFSv4 Server to External Networks

NFSv4 Port Forwarding and External Network Access

NFSv4 significantly simplifies network exposure compared to NFSv3. Where NFSv3 requires managing multiple dynamic ports (mountd, statd, lockd), NFSv4 uses only port 111 (rpcbind) and port 2049 (NFS). This makes firewall configuration and port forwarding straightforward.

For production environments, consider implementing Kerberos authentication (krb5, krb5i, or krb5p) instead of relying solely on network-based access control. However, basic port forwarding remains a valid approach for many deployments.

Network Setup Example

This guide assumes:

• External network: 192.168.0.0/16
• Gateway external IP: 192.168.1.100
• NFS server internal IP: 10.2.2.2
• NFS export path: /nfs/data

Replace these values with your actual network configuration.

Configure Port Forwarding on the Gateway

Set up NAT rules to forward both TCP and UDP traffic for ports 111 and 2049 from the gateway to the internal NFS server:

iptables -t nat -A PREROUTING -d 192.168.1.100/32 -p tcp -m tcp --dport 2049 -j DNAT --to-destination 10.2.2.2:2049
iptables -t nat -A PREROUTING -d 192.168.1.100/32 -p udp -m udp --dport 2049 -j DNAT --to-destination 10.2.2.2:2049
iptables -t nat -A PREROUTING -d 192.168.1.100/32 -p tcp -m tcp --dport 111 -j DNAT --to-destination 10.2.2.2:111
iptables -t nat -A PREROUTING -d 192.168.1.100/32 -p udp -m udp --dport 111 -j DNAT --to-destination 10.2.2.2:111

If you’re using nftables (the modern replacement for iptables), the equivalent rules are:

nft add rule nat prerouting ip daddr 192.168.1.100 tcp dport 2049 dnat to 10.2.2.2:2049
nft add rule nat prerouting ip daddr 192.168.1.100 udp dport 2049 dnat to 10.2.2.2:2049
nft add rule nat prerouting ip daddr 192.168.1.100 tcp dport 111 dnat to 10.2.2.2:111
nft add rule nat prerouting ip daddr 192.168.1.100 udp dport 111 dnat to 10.2.2.2:111

Persist your rules according to your system’s firewall management tool. On systemd-based systems, save iptables rules with iptables-save or use firewalld with permanent rules. For nftables, save the ruleset with nft list ruleset > /etc/nftables.conf.

Configure the NFS Server

On the NFS server (10.2.2.2), edit /etc/exports and add the external network subnet with appropriate permissions:

/nfs/data 192.168.0.0/16(rw,sync,no_root_squash,no_subtree_check)

Key export options explained:

• rw — read/write access
• sync — force synchronous writes (safer than async, standard for production)
• no_root_squash — allows root user on clients to have root privileges on the server (use carefully)
• no_subtree_check — disables subtree checking, improving performance

Apply the configuration:

exportfs -a

Verify the export:

exportfs -v

Output should show:

/nfs/data       192.168.0.0/16(sync,wdelay,hide,no_subtree_check,no_auth_nlm,no_acl,no_root_squash)

Ensure nfs-server is enabled and running:

systemctl enable nfs-server
systemctl start nfs-server

Mount from External Network Client

On a client in the external network (192.168.0.0/16), mount the exported filesystem:

mount -t nfs4 192.168.1.100:/nfs/data /nfs

For NFSv4, specifying the version explicitly with -t nfs4 ensures you’re using version 4 and avoids fallback to older protocols.

Add the mount to /etc/fstab for persistence:

192.168.1.100:/nfs/data /nfs nfs4 defaults,hard,intr,_netdev 0 0

The _netdev option tells the system to wait for network availability before mounting.

Troubleshooting

If the mount fails, verify connectivity to the gateway:

ping 192.168.1.100
telnet 192.168.1.100 2049

Check the NFS server logs:

journalctl -u nfs-server -f

Verify port forwarding rules are active:

iptables -t nat -L -v -n
# or for nftables:
nft list ruleset

Confirm the NFS server is listening on both ports:

ss -tlnp | grep -E ':(111|2049)'

Security Considerations

Network-based access control via IP ranges provides minimal security. For external network access, implement:

• Kerberos authentication (krb5, krb5i, or krb5p flavors)
• VPN tunneling to the internal network
• Host-based firewall rules limiting client access
• Regular auditing of NFS access logs

Using no_root_squash is generally unsafe — consider root_squash (default) unless you have specific requirements for root access from clients.