docs: document 127.0.0.11 embedded DNS server address

Add a brief mention of the embedded DNS server IP address (127.0.0.11)
to the DNS services section of the networking overview. Notes that
there is no IPv6 equivalent and that applications like Nginx can use
this address for explicit DNS configuration.

Fixes #20532

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Signed-off-by: David Karlsson <35727626+dvdksn@users.noreply.github.com>

Author: dvdksn

content/manuals/engine/network/_index.md

@@ -5,16 +5,16 @@ weight: 30
 description: Learn how networking works from the container's point of view
 keywords: networking, container, standalone, IP address, DNS resolution
 aliases:
-- /articles/networking/
-- /config/containers/container-networking/
-- /engine/tutorials/networkingcontainers/
-- /engine/userguide/networking/
-- /engine/userguide/networking/configure-dns/
-- /engine/userguide/networking/default_network/binding/
-- /engine/userguide/networking/default_network/configure-dns/
-- /engine/userguide/networking/default_network/container-communication/
-- /engine/userguide/networking/dockernetworks/
-- /network/
+  - /articles/networking/
+  - /config/containers/container-networking/
+  - /engine/tutorials/networkingcontainers/
+  - /engine/userguide/networking/
+  - /engine/userguide/networking/configure-dns/
+  - /engine/userguide/networking/default_network/binding/
+  - /engine/userguide/networking/default_network/configure-dns/
+  - /engine/userguide/networking/default_network/container-communication/
+  - /engine/userguide/networking/dockernetworks/
+  - /network/
 ---
 
 Container networking refers to the ability for containers to connect to and
@@ -79,7 +79,7 @@ Docker Engine has a number of network drivers, as well as the default "bridge".
 On Linux, the following built-in network drivers are available:
 
 | Driver                          | Description                                                         |
-|:--------------------------------|:--------------------------------------------------------------------|
+| :------------------------------ | :------------------------------------------------------------------ |
 | [bridge](./drivers/bridge.md)   | The default network driver.                                         |
 | [host](./drivers/host.md)       | Remove network isolation between the container and the Docker host. |
 | [none](./drivers/none.md)       | Completely isolate a container from the host and other containers.  |
@@ -192,21 +192,21 @@ These pools can be configured in `/etc/docker/daemon.json`. Docker's built-in de
 ```json
 {
   "default-address-pools": [
-    {"base":"172.17.0.0/16","size":16},
-    {"base":"172.18.0.0/16","size":16},
-    {"base":"172.19.0.0/16","size":16},
-    {"base":"172.20.0.0/14","size":16},
-    {"base":"172.24.0.0/14","size":16},
-    {"base":"172.28.0.0/14","size":16},
-    {"base":"192.168.0.0/16","size":20}
+    { "base": "172.17.0.0/16", "size": 16 },
+    { "base": "172.18.0.0/16", "size": 16 },
+    { "base": "172.19.0.0/16", "size": 16 },
+    { "base": "172.20.0.0/14", "size": 16 },
+    { "base": "172.24.0.0/14", "size": 16 },
+    { "base": "172.28.0.0/14", "size": 16 },
+    { "base": "192.168.0.0/16", "size": 20 }
   ]
 }
 ```
 
 - `base`: The subnet that can be allocated from.
 - `size`: The prefix length used for each allocated subnet.
 
-When an IPv6 subnet is required and there are no IPv6 addresses in  `default-address-pools`, Docker allocates
+When an IPv6 subnet is required and there are no IPv6 addresses in `default-address-pools`, Docker allocates
 subnets from a Unique Local Address (ULA) prefix. To use specific IPv6 subnets instead, add them to your
 `default-address-pools`. See [Dynamic IPv6 subnet allocation](../daemon/ipv6.md#dynamic-ipv6-subnet-allocation)
 for more information.
@@ -222,9 +222,7 @@ Docker will allocate subnets `172.17.0.0/24`, `172.17.1.0/24`, and so on, up to
 
 ```json
 {
-  "default-address-pools": [
-    {"base": "172.17.0.0/16", "size": 24}
-  ]
+  "default-address-pools": [{ "base": "172.17.0.0/16", "size": 24 }]
 }
 ```
 
@@ -265,14 +263,17 @@ Containers that attach to a
 [custom network](drivers/bridge.md#use-user-defined-bridge-networks)
 use Docker's embedded DNS server.
 The embedded DNS server forwards external DNS lookups to the DNS servers configured on the host.
+The embedded DNS server address is `127.0.0.11`.
+There is no IPv6 equivalent; the IPv4 address works even in IPv6-only containers.
+If an application requires an explicit DNS server address, use `127.0.0.11`.
 
 You can configure DNS resolution on a per-container basis, using flags for the
 `docker run` or `docker create` command used to start the container.
 The following table describes the available `docker run` flags related to DNS
 configuration.
 
 | Flag           | Description                                                                                                                                                                                                                                           |
-| -------------- |-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| -------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
 | `--dns`        | The IP address of a DNS server. To specify multiple DNS servers, use multiple `--dns` flags. DNS requests will be forwarded from the container's network namespace so, for example, `--dns=127.0.0.1` refers to the container's own loopback address. |
 | `--dns-search` | A DNS search domain to search non-fully qualified hostnames. To specify multiple DNS search prefixes, use multiple `--dns-search` flags.                                                                                                              |
 | `--dns-opt`    | A key-value pair representing a DNS option and its value. See your operating system's documentation for `resolv.conf` for valid options.                                                                                                              |