Merge pull request #196 from mailcow/shiz0-firststeps-disable_ipv6

Update firststeps-disable_ipv6.md - Added override file and disabling ipv6nat container

docs/firststeps-disable_ipv6.md

@@ -1,19 +1,50 @@
 This is **ONLY** recommended if you do not have an IPv6 enabled network on your host!
 
-If IPv6 MUST be disabled to fit a network, open `docker-compose.yml`, search for `enable_ipv6`...
+If you really need to, you can disable the usage of IPv6 in the compose file.
+Additionally, you can  also disable the startup of container "ipv6nat-mailcow", as it's not needed if you won't use IPv6.
 
+Instead of editing docker-compose.yml directly, it is preferrable to create an override file for it 
+and implement your changes to the service there. Unfortunately, this right now only seems to work for services, not for network settings.
+
+To disable IPv6 on the mailcow network, open docker-compose.yml with your favourite text editor and search for the network section (it's near the bottom of the file). 
+
+Change `enable_ipv6: true` to `enable_ipv6: false`:
 
 ```
 networks:
   mailcow-network:
-    [...]
+    driver: bridge
+    driver_opts:
+      com.docker.network.bridge.name: br-mailcow
     enable_ipv6: true
-    [...]
+    ipam:
+      driver: default
+      config:
+        - subnet: ${IPV4_NETWORK:-172.22.1}.0/24
+        - subnet: ${IPV6_NETWORK:-fd4d:6169:6c63:6f77::/64}
 ```
 
-...change it to `enable_ipv6: false`.
+To disable the ipv6nat-mailcow container as well, go to your mailcow directory and create a new file called "docker-compose.override.yml": 
 
-mailcow needs to be shutdown, the containers removed and the network recreated:
+**NOTE:** If you already have an override file, of course don't recreate it, but merge the lines below into your existing one accordingly!
+
+```
+# cd /opt/mailcow-dockerized
+# touch docker-compose.override.yml
+```
+
+Open the file in your favourite text editor and fill in the following:
+
+```
+version: '2.1'
+services:
+
+    ipv6nat-mailcow:
+      restart: "no"
+      entrypoint: ["echo", "ipv6nat disabled in compose.override.yml"]
+```
+
+For these changes to be effective, you need to fully stop and then restart the stack, so containers and networks are recreated:
 
 ```
 docker-compose down