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How to use TAYGA

If you just want to install / use TAYGA, skip down to Installation

Stateless versus Stateful NAT64

Most people are familiar with stateful NAT, which allows N:1 address mapping by tracking TCP and UDP sessions and rewriting port numbers on each packet. Most commonly this is used to translate sessions from multiple "internal" hosts (which are numbered with private IPv4 addresses) onto a single global IPv4 address on the NAT device's "external" interface.

Stateless NAT does no such session tracking or port number rewriting. It simply performs a 1:1 substitution of IP addresses using a mapping table provided by the network administrator. For example, an organization whose global address allocation was 198.51.100.0/24 but whose hosts were using addresses in 192.0.2.0/24 could use a stateless NAT to rewrite 192.0.2.1 into 198.51.100.1, 192.0.2.35 into 198.51.100.35, etc, in the outbound direction, and the reverse in the inbound direction. This is commonly done when an organization moves to a new ISP and receives a new IPv4 address delegation of the same size as their old delegation but does not want to renumber their network.

TAYGA and other stateless NAT64 translators operate in this fashion. When translating packets between IPv4 and IPv6, the source and destination addresses in the packet headers are substituted using a 1:1 mapping. This means that, in order to exchange packets across the NAT64, each IPv4 host must be represented by a unique IPv6 address, and each IPv6 host must be represented by a unique IPv4 address. How this mapping is performed is discussed in the next sections.

In situations where stateful NAT64 is required, TAYGA can be used in combination with a stateful IPv4 NAT such as the iptables MASQUERADE target. This allows the administrator a great deal more flexibility than if stateful NAT were implemented directly in TAYGA.

Mapping IPv4 into IPv6

TAYGA maps IPv4 addresses into the IPv6 network according to RFC 6052. This states that a 32-bit IPv4 address should be appended to a designated IPv6 prefix, which we call the NAT64 prefix, and the resulting IPv6 address can be used to contact the IPv4 host through the NAT64.

The NAT64 prefix should be assigned out of a site's global IPv6 address allocation. For example, if a site is allocated 2001:db8:1::/48, the prefix 2001:db8:1:ffff::/96 could be set aside for NAT64. (There are several options for the length of the NAT64 prefix, but a /96 is recommended.) The IPv4 host 198.51.100.10 could then be accessed through the NAT64 using the address 2001:db8:1:ffff::c633:640a. Conveniently, it is possible to use the syntax 2001:db8:1:ffff::198.51.100.10 instead.

RFC 6052 also specifies a Well-Known Prefix 64:ff9b::/96 which can be used for NAT64 service rather than allocating a prefix from the site's IPv6 address block. However, this comes with several restrictions, primarily that hosts with private IPv4 addresses (10.x.x.x, 192.168.x.x, etc) cannot be accessed through the NAT64. See RFC 6052 for more information.

If NAT64 service is needed for only a few hosts instead of the entire IPv4 address space, TAYGA can be configured without a NAT64 prefix, and address maps can be assigned on a host-by-host basis.

Mapping IPv6 into IPv4

Being a stateless NAT, TAYGA requires that a unique IPv4 address is assigned to every IPv6 host that needs NAT64 service. This assignment can be done statically by the network administrator, or dynamically by TAYGA from a pool of IPv4 addresses designated for this purpose.

Static address mapping is desirable for servers or other hosts requiring a well-known address. Statically mapped addresses may be entered into DNS, for example.

Dynamic address mapping allows TAYGA to assign IPv4 addresses to IPv6 hosts as they are needed. By default, these assignments are guaranteed to remain usable for up to two hours after the last packet seen, but they are retained for up to two weeks as long as the address pool does not become empty. Assignments are written to disk so they persist through a restart of the TAYGA daemon, allowing existing TCP and UDP sessions to continue uninterrupted.

(Of course, TAYGA also supports the addressing architecture described in RFC 6052 in which IPv6 hosts are numbered with "IPv4-translatable IPv6 addresses" carved out of the NAT64 prefix.)

The log dyn option allows the dynamic mapping assignments to be printed to the service log, if your network requires this information

Installation & Basic Configuration

tayga requires GNU make to build.

git clone git@github.com:apalrd/tayga.git
cd tayga
make

This will build the tayga executable in the current directory. Installation options will be available in future releases.

Next, if you would like dynamic maps to be persistent between TAYGA restarts, create a directory to store the dynamic.map file:

mkdir -p /var/db/tayga

Now create your site-specific tayga.conf configuration file. The installed tayga.conf.example file can be copied to tayga.conf and modified to suit your site. Here is a sample minimal configuration:

tun-device nat64
ipv4-addr 192.168.255.1
prefix 2001:db8:1:ffff::/96     # replace with a prefix from
                                # your site's address range
dynamic-pool 192.168.255.0/24
data-dir /var/db/tayga          # omit if you do not need persistent
                                # dynamic address maps

Before starting the tayga daemon, the routing setup on your system will need to be changed to send IPv4 and IPv6 packets to tayga. First create the TUN network interface:

tayga --mktun

If tayga prints any errors, you will need to fix your config file before continuing. Otherwise, the new nat64 interface can be configured and the proper routes can be added to your system:

ip link set nat64 up
ip addr add 2001:db8:1::1 dev nat64  # replace with your router's address
ip addr add 192.168.0.1 dev nat64    # replace with your router's address
ip route add 2001:db8:1:ffff::/96 dev nat64  # from tayga.conf
ip route add 192.168.255.0/24 dev nat64      # from tayga.conf

Firewalling your NAT64 prefix from outside access is highly recommended:

ip6tables -A FORWARD -s 2001:db8:1::/48 -d 2001:db8:1:ffff::/96 -j ACCEPT
ip6tables -A FORWARD -d 2001:db8:1:ffff::/96 -j DROP

At this point, you may start the tayga process:

tayga

Check your system log (/var/log/syslog or /var/log/messages) for status information.

If you are having difficulty configuring tayga, use the -d option to run the tayga process in the foreground and send all log messages to stdout:

tayga -d

Usage Guides

Many example configurations are provided, each with an example tayga.conf as well as a shell script to launch the configuraton on Linux (assuming basic iproute2 network setup and iptables). Feel free to reference all of these examples for your own configuration.