dev: NixOS 25.11 매뉴얼 로컬 사본 추가

nixpkgs nixos-25.11 브랜치의 nixos/doc/manual/ 디렉토리를 sparse clone으로
가져와 ~/obsidian/dev/nixos-manual/에 복사. _index.md에 구조/갱신 방법 정리.

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빠른 참조로 사용.

dev/nixos-manual/configuration/ipv6-config.section.md

@@ -0,0 +1,48 @@
+# IPv6 Configuration {#sec-ipv6}
+
+IPv6 is enabled by default. Stateless address autoconfiguration is used
+to automatically assign IPv6 addresses to all interfaces, and Privacy
+Extensions (RFC 4941) are enabled by default. You can adjust the default
+for this by setting [](#opt-networking.tempAddresses). This option
+may be overridden on a per-interface basis by
+[](#opt-networking.interfaces._name_.tempAddress). You can disable
+IPv6 support globally by setting:
+
+```nix
+{ networking.enableIPv6 = false; }
+```
+
+You can disable IPv6 on a single interface using a normal sysctl (in
+this example, we use interface `eth0`):
+
+```nix
+{ boot.kernel.sysctl."net.ipv6.conf.eth0.disable_ipv6" = true; }
+```
+
+As with IPv4 networking interfaces are automatically configured via
+DHCPv6. You can configure an interface manually:
+
+```nix
+{
+  networking.interfaces.eth0.ipv6.addresses = [
+    {
+      address = "fe00:aa:bb:cc::2";
+      prefixLength = 64;
+    }
+  ];
+}
+```
+
+For configuring a gateway, optionally with explicitly specified
+interface:
+
+```nix
+{
+  networking.defaultGateway6 = {
+    address = "fe00::1";
+    interface = "enp0s3";
+  };
+}
+```
+
+See [](#sec-ipv4) for similar examples and additional information.