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>
<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>