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<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>NPTv6 (IPv6-to-IPv6 Network Prefix Translation) for Linux</title><meta name="generator" content="DocBook XSL Stylesheets V1.76.1" /></head><body><div class="article" title="NPTv6 (IPv6-to-IPv6 Network Prefix Translation) for Linux"><div class="titlepage"><div><div><h2 class="title"><a id="id315566"></a>NPTv6 (IPv6-to-IPv6 Network Prefix Translation) for Linux</h2></div><div><div class="author"><h3 class="author"><span class="firstname">Sven-Ola</span> <span class="surname">Tuecke</span></h3><div class="affiliation"><span class="orgname">Freifunk<br /></span></div></div></div><div><div class="author"><h3 class="author"><span class="firstname">Matthias</span> <span class="surname">Schiffer</span></h3><div class="affiliation"><span class="orgname">Freifunk Lübeck<br /></span></div></div></div><div><p class="pubdate">10-NOV-2011</p></div></div><hr /></div><div class="toc"><p><strong>Table of Contents</strong></p><dl><dt><span class="section"><a href="#install">Installation</a></span></dt><dt><span class="section"><a href="#dkms">DKMS Integration</a></span></dt><dt><span class="section"><a href="#config">Configuration</a></span></dt><dd><dl><dt><span class="section"><a href="#config-brief">Brief Version</a></span></dt></dl></dd><dt><span class="section"><a href="#precedence">IPv6/IPv4 Precedence</a></span></dt><dd><dl><dt><span class="section"><a href="#precedence-gai">Change gai.conf</a></span></dt><dt><span class="section"><a href="#precedence-addrs">Use Changed Internal Address</a></span></dt></dl></dd><dt><span class="section"><a href="#motivation">Motivation</a></span></dt></dl></div><p>These files implement a Linux netfilter target that changes the IPv6
  address of packets. The address change is done checksum neutral, thus no
  checksum re-calculation for the packet is necessary. You can change the IPv6
  source address of outgoing packets as well as the IPv6 destination address
  of incoming packets. This allows you to map an internal IPv6 address range
  to a second, externally used IPv6 address range. IPv6 address mapping is not
  very similar to IPv4 network address translation, but one can describe it as
  some sort of stateless NAT. The implementation is based on the expired IETF
  discussion paper published here:</p><p><a class="ulink" href="https://tools.ietf.org/html/rfc6296" target="_top">https://tools.ietf.org/html/rfc6296</a></p><div class="warning" title="Warning" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Warning</h3><p>Using NPTv6 rules together with connection tracking rules such as
    <strong class="userinput"><code>--ctstate</code></strong> is currently untested and may not work or
    may cause dysfunctions.</p></div><div class="section" title="Installation"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="install"></a>Installation</h2></div></div></div><p>NPTv6 implements two pieces of software: a shared library that
    extends the ip6tables command and a Linux kernel module. The shared
    library file adds the '-j SNPTV6' target (for source address translation)
    and the '-j DNPTV6' target (for destination address translation) to the
    ip6tables command. To build and install, you need ip6tables installed as
    well as the necessary headers. The Linux kernel module requires the Linux
    source file tree and kernel configuration files to compile. On a Debian/(EKU)buntu,
    the following command prepares the build environment:</p><pre class="programlisting">sudo apt-get install build-essential linux-headers iptables-dev</pre><p>Unpack the source tgz archive below <code class="filename">/usr/src</code>,
    change to the new sub-directory and issue "make" to build. If this
    compiles without errors, install the ip6tabless extension by copying
    libip6t_SNPTV6.so and libip6t_DNPTV6.so to the iptables module directory,
    which is probably located under <code class="filename">/lib/xtables</code> or
    <code class="filename">/usr/lib/iptables</code>.</p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>The kernel module (<code class="filename">ip6t_MAP66.ko</code> is not
      automatically installed nor loaded into the kernel. You can copy the
      kernel module file manually, e.g. with <strong class="userinput"><code>sudo cp ip6t_MAP66.ko
      /lib/modules/$(uname -r)/</code></strong>.</p></div></div><div class="section" title="DKMS Integration"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="dkms"></a>DKMS Integration</h2></div></div></div><p>If the next system update needs to install a new kernel version, you
    also need to re-compile/re-install the MAP66 kernel module. With
    Debian/(EKU)buntu, this can be automated with the Dynamic Kernel Module
    Support Framework (DKMS). For this, the <code class="filename">dkms.conf</code>
    file is included with the MAP66 source file package. Install DKMS with the
    following command:</p><pre class="programlisting">sudo apt-get install dkms</pre><p>If not already in place, move/unpack the MAP66 source file archive
    below <code class="filename">/usr/src/</code>. To register the MAP66 source to DKMS
    and compile/install, issue these commands:</p><pre class="programlisting">sudo dkms add -m ip6t_NPTV6 -v 0.6
sudo dkms build -m ip6t_NPTV6 -v 0.6
sudo dkms install -m ip6t_NPTV6 -v 0.6</pre><p>Read DKMS details here: <a class="ulink" href="Read DKMS details here: https://wiki.kubuntu.org/Kernel/Dev/DKMSPackaging" target="_top">https://wiki.kubuntu.org/Kernel/Dev/DKMSPackaging</a></p></div><div class="section" title="Configuration"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="config"></a>Configuration</h2></div></div></div><div class="section" title="Brief Version"><div class="titlepage"><div><div><h3 class="title"><a id="config-brief"></a>Brief Version</h3></div></div></div><p>You always need to add two ip6tables-rules to your netfilter
      configuration. One rule matches outgoing packets and changes their IPv6
      source address. The second rule matches incoming packets and reverts the
      address change by altering their IPv6 destination address. To following
      commands correspond to the <span class="quote">“<span class="quote">Address Mapping Example</span>”</span> given
      in the IETF discussion paper:</p><pre class="programlisting">ip6tables -t mangle -I POSTROUTING -o eth0 -s FD01:0203:0405::/48 -j SNPTV6 --to-source 2001:0DB8:0001::/48
ip6tables -t mangle -I PREROUTING  -i eth0 -d 2001:0DB8:0001::/48 -j DNPTV6 --to-destination FD01:0203:0405::/48</pre><p>This example is also printed to the screen if you issue
      <strong class="userinput"><code>ip6tables -j SNPTV6 --help</code></strong>. By design, you cannot
      use prefix lengths longer than 64.</p></div></div><div class="section" title="IPv6/IPv4 Precedence"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="precedence"></a>IPv6/IPv4 Precedence</h2></div></div></div><p>With (EKU)buntu and eventually with RedHat, you will notice that
    your browser does not show the IPv6 version of a web site that is
    multi-homed when using ULA addresses for your IPv6 Internet connection.
    The reason for this is an add on to the RFC 3484 rules that is compiled
    into the (EKU)buntu libc. The pre-installed
    <code class="filename">/etc/gai.conf</code> file will give you a hint on
    this.</p><p>In short: the getaddrinfo() library function rates a private IPv4
    address higher than the ULA IPv6 address when choosing the transport
    protocol for a new Internet connection if this add on to the RFC 3484
    rules is compiled in. For this reason, you may want to change the
    precedence rules within <code class="filename">/etc/gai.conf</code> (see <a class="xref" href="#precedence-gai" title="Change gai.conf">Change gai.conf</a>) or use another
    prefix (see <a class="xref" href="#precedence-addrs" title="Use Changed Internal Address">Use Changed Internal Address</a>).</p><div class="section" title="Change gai.conf"><div class="titlepage"><div><div><h3 class="title"><a id="precedence-gai"></a>Change gai.conf</h3></div></div></div><p>The getaddrinfo() library function manages lists of label,
      precedence, and scope4 type entries. If the
      <code class="filename">/etc/gai.conf</code> file does not provide a single entry
      for a particular type, the compiled-in list is used. For this reason,
      you cannot uncomment a single entry to overwrite the default. You need
      to uncomment all entries of a particular type for this. The
      <span class="quote">“<span class="quote">label</span>”</span> lines compare source addresses, the
      <span class="quote">“<span class="quote">precedence</span>”</span> lines compare destination addresses.</p><div class="procedure" title="Procedure 1. Change IPv6 Precedence"><a id="id314638"></a><p class="title"><strong>Procedure 1. Change IPv6 Precedence</strong></p><ol class="procedure" type="1"><li class="step" title="Step 1"><p>Open the <code class="filename">/etc/gai.conf</code> file as root user,
          e.g. by executing <strong class="userinput"><code>sudo nano
          /etc/gai.conf</code></strong>.</p></li><li class="step" title="Step 2"><p>Remove the leading hash character from the 8 lines starting
          with <span class="quote">“<span class="quote">#label</span>”</span>.</p></li><li class="step" title="Step 3"><p>Re-add the hash character to the line stating <span class="quote">“<span class="quote">#label
          fc00::/7 6</span>”</span>.</p></li><li class="step" title="Step 4"><p>Save the file.</p></li><li class="step" title="Step 5"><p>Restart your browser and re-try to browse to a multi-homed web
          site.</p></li></ol></div><p>The above procedure removes the difference between standard IPv6
      source addresses and ULA type private IPv6 source addresses. Anything
      else is unchanged.</p></div><div class="section" title="Use Changed Internal Address"><div class="titlepage"><div><div><h3 class="title"><a id="precedence-addrs"></a>Use Changed Internal Address</h3></div></div></div><p>As an alternative solution, you may use an arbitrary address
      prefix in your LAN that is not mentioned in the
      <code class="filename">gai.conf</code> file nor compiled in. This will work but
      introduces a double mapping: one map (Inet-ULA) on the Internet gateway
      router and a second map (ULA-Intern) on the internal router. </p><div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p>While the well known IPv4 addresses 10.0.0.0/8, 172.16.0.0/12,
        and 192.168.0.0/16 still exist, it is unlikely that their 6to4
        counterparts 2002:0a00::/24, 2002:ac10::/28, and 2002:c0a8::/32 will
        be routed on the Internet. Sadly, the (EKU)buntu defaults penalize
        6to4 addresses also.</p></div><p>If you already deployed ULA addresses in your network, you may be
      interested in a solution that runs on my Freifunk router. The router
      uses the IPv6 prefix that is reserved for documentation purposes on it's
      LAN interface. Within the OLSR-based mesh network, any interface uses an
      fdca:ffee:babe::/64 prefix. The following internal mapping is configured
      for this:</p><pre class="programlisting">ip6tables -t mangle -I PREROUTING -i br0 -s 2001:0DB8::/64 -j MAP66 --src-to fdca:ffee:babe::/64 --csum
ip6tables -t mangle -I POSTROUTING -o br0 -d fdca:ffee:babe::/64 -j MAP66 --dst-to 2001:0DB8::/64 --csum</pre><p>To prevent the mapped packets to vanish via the default route and
      to overcome mac address lookups during the routing process, I also added
      these prefixes to the router's <code class="filename">/etc/radvd.conf</code> as
      well as (host) routes pointing to the <span class="quote">“<span class="quote">br0</span>”</span> interface for
      both prefixes.</p></div></div><div class="section" title="Motivation"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="motivation"></a>Motivation</h2></div></div></div><p>My Internet access at home is realized by a wireless community mesh
    network not owned by me. The mesh is operated with small embedded devices
    (nodes aka. WLAN routers) that are interconnected via radio links (WLAN
    IBSS / AdHoc). Routing is done with a specialized protocol such as Batman
    or OLSR. The routing protocol selects the nearest out of a dozen Internet
    gateways and configures a default route or an IPIP tunnel accordingly.
    Each Internet gateway is connected to a different ISP and provides the
    service with the help of IPv4 network address translation (NAT). Using NAT
    has the following effects:</p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>Address amplification - something not necessary with IPv6 any
        more</p></li><li class="listitem"><p>Anonymization - nice to have as an option but not mission
        critical</p></li><li class="listitem"><p>ISP independence - no reverse routing, no
        "buy-a-number-range"</p></li></ul></div><p>The last point <span class="bold"><strong>is</strong></span> mission critical.
    One can obtain a provider independent IPv6 address range, but you need the
    cooperation of an ISP to use that address range for Internet connectivity.
    If you e.g. move to another ISP you need your address range to be
    re-routed to your new location.</p><p>ISP independence is also possible with some tunneling technique,
    such as VPN or mobile IP. Tunneling can be implemented on client PCs and
    Internet gateways/servers one day. But there is no need to implement the
    same tunneling technique on every mesh node. Why? Because the mesh nodes
    can use private IP addresses (or "ULA") to transport the tunnel data
    between the client PC and the gateway/server. Each tunneling technique
    typically needs a single instance (the "server") which forms a single
    point of failure. Rule-of-thumb1: avoid a SPOF for the infrastructure.
    Rule-of-thumb2: KISS (keep it simple stupid).</p><p>Using private IP addresses on the mesh nodes has a drawback: mesh
    node software updates e.g. a download via HTTP from an Internet server is
    not possible. This is where I start to think: <span class="quote">“<span class="quote">hey, some kind of
    address mapping may be nice to have</span>”</span>. While opening Pandora's NAT66
    box, I discovered that IPv6 nerds do not like the acronym. It is always a
    good tactic in info wars to rename, hence the name "MAP66".</p><p>// Sven-Ola</p></div></div></body></html>