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, and Privacy
  Extensions (RFC 4946) are enabled by default. You can adjust the default
  for this by setting <xref linkend="opt-networking.tempAddresses"/>.
  This option may be overridden on a per-interface basis by
  <xref linkend="opt-networking.interfaces._name_.tempAddress"/>.
  You can disable IPv6 support globally by setting:
<programlisting>
<xref linkend="opt-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>
<xref linkend="opt-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>
<link linkend="opt-networking.interfaces._name_.ipv6.addresses">networking.interfaces.eth0.ipv6.addresses</link> = [ {
  address = "fe00:aa:bb:cc::2";
  prefixLength = 64;
} ];
</programlisting>
 </para>

 <para>
  For configuring a gateway, optionally with explicitly specified interface:
<programlisting>
<xref linkend="opt-networking.defaultGateway6"/> = {
  address = "fe00::1";
  interface = "enp0s3";
};
</programlisting>
 </para>

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