Allow NFS through iptables on a RedHat system

This post describes how you can configure your RedHat Enterprise WS 4 NFS system behind a iptables firewall to be available for clients outside the firewall on a permanent basis.

Symptom
NFS relies on portmap to assign the ports on which it will listen. One side effect of this is that the ports are randomly assigned, so each time NFS is restarted the ports will change. This can make it difficult to run an NFS server behind a firewall which only allows access to specific ports on the system.

Solution
The first step is to assign a permanent port number to each of the NFS services (rquotad, mountd, statd, and lockd). While they can use any unused ports greater than 1024, it is recommended that you first consult the file /etc/services to find a valid unused port range. The following examples use the range 10000-10005.

The majority of the ports are configured through the file /etc/sysconfig/nfs. You will need to create this file if it does not exist. It should look similar to the following example:

# NFS port numbers
STATD_PORT=10002
STATD_OUTGOING_PORT=10003
MOUNTD_PORT=10004
RQUOTAD_PORT=10005

The lockd service is configured differently from the others because it is compiled as a kernel module. To set the port which lockd uses, add these options in the /etc/sysconfig/nfs file:

LOCKD_UDPPORT=30001
LOCKD_TCPPORT=30001

where “30001″ can be replaced with any port that is available and can be assigned for use.

After these configuration changes, you can view the port assignments with the command rpcinfo -p

# rpcinfo -p | awk -F " " '{print $3 ", " $4 ", " $5}' | sort | uniq
   proto, port,
tcp, 111, portmapper
tcp, 2049, nfs
tcp, 32771, nlockmgr
tcp, 800, rquotad
tcp, 814, mountd
udp, 111, portmapper
udp, 2049, nfs
udp, 32768, nlockmgr
udp, 797, rquotad
udp, 811, mountd

At this point, the ports will remain the same when NFS is restarted. The following is a list of ports which need to be opened on the firewall:

proto, port,
tcp, 10004, mountd
tcp, 10005, rquotad
tcp, 111, portmapper
tcp, 2049, nfs
tcp, 32771, nlockmgr
udp, 10004, mountd
udp, 10005, rquotad
udp, 111, portmapper
udp, 2049, nfs
udp, 32768, nlockmgr

You can now open these ports on the firewall to allow remote clients to mount a share on the server. If you are using iptables, the following commands can be used to add inbound/outbound rules to allow access to these ports.
Note that this is only an example, as your specific firewall rules may differ.
This is an excerp of my /etc/sysconfig/iptables file. It allows NFS connections from IP address 192.168.0.10 but doesn’t restrict traffic out.

-A RH-Firewall-1-INPUT -s 192.168.0.10 -p tcp -m tcp --dport 111 -j ACCEPT
-A RH-Firewall-1-INPUT -s 192.168.0.10 -p udp -m udp --dport 111 -j ACCEPT
-A RH-Firewall-1-INPUT -s 192.168.0.10  -p tcp -m tcp --dport 2049 -j ACCEPT
-A RH-Firewall-1-INPUT -s 192.168.0.10 -p udp -m udp --dport 2049 -j ACCEPT
-A RH-Firewall-1-INPUT -s 192.168.0.10 -p tcp -m tcp --dport 10000 -j ACCEPT
-A RH-Firewall-1-INPUT -s 192.168.0.10 -p udp -m udp --dport 10001 -j ACCEPT
-A RH-Firewall-1-INPUT -s 192.168.0.10 -p tcp -m tcp --dport 10002:10005 -j ACCEPT
-A RH-Firewall-1-INPUT -s 192.168.0.10 -p udp -m udp --dport 10002:10005 -j ACCEPT
-A RH-Firewall-1-INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
-A RH-Firewall-1-INPUT -i eth0 -p tcp -m tcp -j LOG --log-prefix "Reject Traffic " --log-level 6
-A RH-Firewall-1-INPUT -i eth0 -p tcp -m tcp -j REJECT --reject-with icmp-port-unreachable

This post is a modified example of the solution from RedHat Knowledgebase Article ID 5928.

2 thoughts on “Allow NFS through iptables on a RedHat system”

  1. Everything works, except for the tag “RH-Firewall-1-INPUT”.

    I got this error:
    iptables: Applying firewall rules: iptables-restore: line 13 failed

    Line 13 was the first line of the NFS rules.

    I just changed it to “INPUT” and it worked.
    My iptables now looks like this:
    http://pastebin.com/FLRT8jQK

    I guess this is a change between CentOS 5 and CentOS 6?

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