9.7.3. Running NFS Behind a Firewall

NFS requires rpcbind, which dynamically assigns ports for RPC services and can cause problems for configuring firewall rules. To allow clients to access NFS shares behind a firewall, edit the /etc/sysconfig/nfs configuration file to control which ports the required RPC services run on.
The /etc/sysconfig/nfs may not exist by default on all systems. If it does not exist, create it and add the following variables, replacing port with an unused port number (alternatively, if the file exists, un-comment and change the default entries as required):
MOUNTD_PORT=port
Controls which TCP and UDP port mountd (rpc.mountd) uses.
STATD_PORT=port
Controls which TCP and UDP port status (rpc.statd) uses.
LOCKD_TCPPORT=port
Controls which TCP port nlockmgr (lockd) uses.
LOCKD_UDPPORT=port
Controls which UDP port nlockmgr (lockd) uses.
If NFS fails to start, check /var/log/messages. Normally, NFS will fail to start if you specify a port number that is already in use. After editing /etc/sysconfig/nfs, restart the NFS service using service nfs restart. Run the rpcinfo -p command to confirm the changes.
To configure a firewall to allow NFS, perform the following steps:

Procedure 9.1. Configure a firewall to allow NFS

  1. Allow TCP and UDP port 2049 for NFS.
  2. Allow TCP and UDP port 111 (rpcbind/sunrpc).
  3. Allow the TCP and UDP port specified with MOUNTD_PORT="port"
  4. Allow the TCP and UDP port specified with STATD_PORT="port"
  5. Allow the TCP port specified with LOCKD_TCPPORT="port"
  6. Allow the UDP port specified with LOCKD_UDPPORT="port"

Note

To allow NFSv4.0 callbacks to pass through firewalls set /proc/sys/fs/nfs/nfs_callback_tcpport and allow the server to connect to that port on the client.
This process is not needed for NFSv4.1 or higher, and the other ports for mountd, statd, and lockd are not required in a pure NFSv4 environment.

9.7.3.1. Discovering NFS exports

There are two ways to discover which file systmes an NFS server exports.
First, on any server that supports NFSv2 or NFSv3, use the showmount command:
$ showmount -e myserver
Export list for mysever
/exports/foo
/exports/bar
Second, on any server that supports NFSv4, mount / and look around.
# mount myserver:/ /mnt/
#cd /mnt/
exports
# ls exports
foo
bar
On servers that support both NFSv4 and either NFSv2 or NFSv3, both methods will work and give the same results.

Note

Before Red Hat Enterprise Linux 6 on older NFS servers, depending on how they are configured, it is possible to export filesystems to NFSv4 clients at different paths. Because these servers do not enable NFSv4 by default this should not normally be a problem.