Documentation > Basic Tutorials > Stateful NAT64

Stateful NAT64 Run


  1. Introduction
  2. Sample Network
  3. Jool
  4. Testing
  5. Stopping Jool
  6. Afterwords


This document explains how to run Jool in Stateful NAT64 mode.

Software-wise, only a successful install of the kernel module is required. The userspace application is not needed in this basic run.

Sample Network

Figure 1 - Sample Network

All the remarks in the first document’s Sample Network section apply here.

Nodes A through E:

user@A:~# service network-manager stop
user@A:~# /sbin/ip link set eth0 up
user@A:~# # Replace "::8" depending on which node you're on.
user@A:~# /sbin/ip address add 2001:db8::8/96 dev eth0
user@A:~# /sbin/ip route add default via 2001:db8::1

Nodes V through Z:

user@V:~# service network-manager stop
user@V:~# /sbin/ip link set eth0 up
user@V:~# # Replace ".16" depending on which node you're on.
user@V:~# /sbin/ip address add dev eth0

Notice these nodes do not need a default route. This is a consequence of them being in the same network as the NAT64; T will be masking the IPv6 nodes, so V through Z think they’re talking directly to it.

Node T:

user@T:~# service network-manager stop
user@T:~# /sbin/ip link set eth0 up
user@T:~# /sbin/ip address add 2001:db8::1/96 dev eth0
user@T:~# /sbin/ip link set eth1 up
user@T:~# /sbin/ip address add dev eth1
user@T:~# sysctl -w net.ipv4.conf.all.forwarding=1
user@T:~# sysctl -w net.ipv6.conf.all.forwarding=1
user@T:~# ethtool --offload eth0 gro off
user@T:~# ethtool --offload eth0 lro off
user@T:~# ethtool --offload eth1 gro off
user@T:~# ethtool --offload eth1 lro off

Note! In previous versions of Jool, T used to need two or more IPv4 addresses. Because pool4 now stores port ranges, this is no longer the case.

Remember you might want to cross-ping T vs everything before continuing.


This is the insertion syntax:

Most Distros OpenWRT
user@T:~# /sbin/modprobe [--first-time] jool \
		[pool6=<IPv6 prefix>] \
		[pool4=<IPv4 prefixes>] \
user@T:~# insmod jool \
		[pool6=<IPv6 prefix>] \
		[pool4=<IPv4 prefixes>] \

See Kernel Module Options for a description of each argument.

The result looks like this:

Most Distros OpenWRT
user@T:~# /sbin/modprobe --first-time jool pool6=64:ff9b::/96
user@T:~# insmod jool pool6=64:ff9b::/96

Jool will append and remove prefix 64:ff9b::/96.

Note! In previous versions of Jool, pool4 used to be mandatory. This is no longer the case.

Note! Because we skipped the pool4 argument, Jool will fall back to mask packets using the upper ports of Unless you have few IPv6 clients, this is probably not what you want. See pool4 for details on how to fine-tune this.


If something doesn’t work, try the FAQ.

Test by sending requests from the IPv6 network:

user@C:~$ ping6 64:ff9b::
PING 64:ff9b:: 56 data bytes
64 bytes from 64:ff9b::cb00:7110: icmp_seq=1 ttl=63 time=1.13 ms
64 bytes from 64:ff9b::cb00:7110: icmp_seq=2 ttl=63 time=4.48 ms
64 bytes from 64:ff9b::cb00:7110: icmp_seq=3 ttl=63 time=15.6 ms
64 bytes from 64:ff9b::cb00:7110: icmp_seq=4 ttl=63 time=4.89 ms
--- 64:ff9b:: ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3004ms
rtt min/avg/max/mdev = 1.136/6.528/15.603/5.438 ms

Figure 1 - IPv4 TCP from an IPv6 node

Note! Obviously, users should not need to be aware of IP addresses, much less know they need to append a prefix whenever they need to speak to IPv4. The DNS64 document will tell you how to make the prefix-address-hack transparent to users.

Note! Because a NAT64 is stateful, only IPv6-started tests can be run at this point. See port forwarding if 4-to-6 translation is relevant for you.

Stopping Jool

To shut down Jool, revert the modprobe using the -r flag:

Most Distros OpenWRT
user@T:~# /sbin/modprobe -r jool
user@T:~# rmmod jool


  1. More complex setups might require you to consider the MTU notes.
  2. The modprobe insertion and removal mechanism is fine if all you need is a simple single NAT64, but if you want to enclose it in a network namespace, or need multiple Jool instances in a single machine, check out --instance.
  3. Please note that none of what was done in this tutorial survives reboots! Documentation on persistence will be released in the future.

The next tutorial explains DNS64.