nixpkgs/nixos/doc/manual/configuration/ipv6-config.xml

<section xmlns="http://docbook.org/ns/docbook"
         xmlns:xlink="http://www.w3.org/1999/xlink"
         xmlns:xi="http://www.w3.org/2001/XInclude"
         version="5.0"
         xml:id="sec-ipv6">

<title>IPv6 Configuration</title>

<para>IPv6 is enabled by default.  Stateless address autoconfiguration
is used to automatically assign IPv6 addresses to all interfaces.  You
can disable IPv6 support globally by setting:

<programlisting>
networking.enableIPv6 = false;
</programlisting></para>

<para>You can disable IPv6 on a single interface using a normal sysctl (in this
example, we use interface <varname>eth0</varname>):

<programlisting>
boot.kernel.sysctl."net.ipv6.conf.eth0.disable_ipv6" = true;
</programlisting>
</para>

<para>As with IPv4 networking interfaces are automatically configured via
DHCPv6. You can configure an interface manually:

<programlisting>
networking.interfaces.eth0.ip6 = [ { address = "fe00:aa:bb:cc::2"; prefixLength = 64; } ];
</programlisting>
</para>

<para>For configuring a gateway, optionally with explicitly specified interface:

<programlisting>
networking.defaultGateway6 = {
  address = "fe00::1";
  interface = "enp0s3";
}
</programlisting>
</para>

<para>See <xref linkend='sec-ipv4' /> for similar examples and additional information.
</para>

</section>