Docs: host-gateway-ip daemon option IPv4+IPv6

The host-gateway-ip daemon option now accepts two addresses, one IPv4 and one IPv6. Signed-off-by: Rob Murray <[email protected]>
docker · Nov 27, 2024 · f92dc3f · f92dc3f
1 parent 917d2dc
commit f92dc3f
Showing 1 changed file with 18 additions and 6 deletions.
diff --git a/docs/reference/dockerd.md b/docs/reference/dockerd.md
@@ -62,8 +62,7 @@ Options:
   -G, --group string                          Group for the unix socket (default "docker")
       --help                                  Print usage
   -H, --host list                             Daemon socket(s) to connect to
-      --host-gateway-ip ip                    IP address that the special 'host-gateway' string in --add-host resolves to.
-                                              Defaults to the IP address of the default bridge
+      --host-gateway-ip list                  IP addresses that the special 'host-gateway' string in --add-host resolves to. Defaults to the IP addresses of the default bridge
       --http-proxy string                     HTTP proxy URL to use for outgoing traffic
       --https-proxy string                    HTTPS proxy URL to use for outgoing traffic
       --icc                                   Enable inter-container communication (default true)
@@ -837,21 +836,34 @@ For details about how to use this feature, as well as limitations, see
 
 The Docker daemon supports a special `host-gateway` value for the `--add-host`
 flag for the `docker run` and `docker build` commands. This value resolves to
-the host's gateway IP and lets containers connect to services running on the
+addresses on the host, so that containers can connect to services running on the
 host.
 
-By default, `host-gateway` resolves to the IP address of the default bridge.
+By default, `host-gateway` resolves to the IPv4 address of the default bridge,
+and its IPv6 address if it has one.
+
 You can configure this to resolve to a different IP using the `--host-gateway-ip`
 flag for the dockerd command line interface, or the `host-gateway-ip` key in
 the daemon configuration file.
 
+To supply both IPv4 and IPv6 addresses on the command line, use two
+`--host-gateway-ip` options.
+
+To supply two addresses in the daemon configuration file, include two addresses
+in the JSON array, as shown below. For compatibility with older versions of the
+daemon, a single IP address can also be specified in a JSON string rather than
+an array.
+
 ```console
 $ cat > /etc/docker/daemon.json
-{ "host-gateway-ip": "192.0.2.0" }
+{ "host-gateway-ip": ["192.0.2.1", "2001:db8::1111"]}
 $ sudo systemctl restart docker
 $ docker run -it --add-host host.docker.internal:host-gateway \
   busybox ping host.docker.internal 
-PING host.docker.internal (192.0.2.0): 56 data bytes
+PING host.docker.internal (192.0.2.1): 56 data bytes
+$ docker run -it --add-host host.docker.internal:host-gateway \
+  busybox ping -6 host.docker.internal
+PING host.docker.internal (2001:db8::1111): 56 data bytes
 ```
 
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