Small fixes in DNS documentation

docs/configuring-dns.md

@@ -32,14 +32,14 @@ DNS records marked with `(*)` above are optional. They refer to services that wi
 
 ## Subdomains setup
 
-As the table above illustrates, you need to create 2 subdomains (`matrix.<your-domain>` and `riot.<your-domain>`) and point both of them to your new server's IP address (DNS `A` record or `CNAME` record is fine).
+As the table above illustrates, you need to create 2 subdomains (`matrix.<your-domain>` and `riot.matrix.<your-domain>`) and point both of them to your new server's IP address (DNS `A` record or `CNAME` record is fine).
 
-The `riot.<your-domain>` subdomain is necessary, because this playbook installs the Riot web client for you.
-If you'd rather instruct the playbook not to install Riot (`matrix_riot_web_enabled: false` when [Configuring the playbook](configuring-playbook.md) later), feel free to skip the `riot.<your-domain>` DNS record.
+The `riot.matrix.<your-domain>` subdomain is necessary, because this playbook installs the Riot web client for you.
+If you'd rather instruct the playbook not to install Riot (`matrix_riot_web_enabled: false` when [Configuring the playbook](configuring-playbook.md) later), feel free to skip the `riot.matrix.<your-domain>` DNS record.
 
-The `dimension.<your-domain>` subdomain may be necessary, because this playbook could install the [Dimension integrations manager](http://dimension.t2bot.io/) for you. Dimension installation is disabled by default, because it's only possible to install it after the other Matrix services are working (see [Setting up Dimension](configuring-playbook-dimension.md) later). If you do not wish to set up Dimension, feel free to skip the `dimension.<your-domain>` DNS record.
+The `dimension.matrix.<your-domain>` subdomain may be necessary, because this playbook could install the [Dimension integrations manager](http://dimension.t2bot.io/) for you. Dimension installation is disabled by default, because it's only possible to install it after the other Matrix services are working (see [Setting up Dimension](configuring-playbook-dimension.md) later). If you do not wish to set up Dimension, feel free to skip the `dimension.matrix.<your-domain>` DNS record.
 
-The `jitsi.<your-domain>` subdomain may be necessary, because this playbook could install the [Jitsi video-conferencing platform](https://jitsi.org/) for you. Jitsi installation is disabled by default, because it may be heavy and is not a core required component. To learn how to install it, see our [Jitsi](configuring-playbook-jitsi.md) guide. If you do not wish to set up Jitsi, feel free to skip the `jitsi.<your-domain>` DNS record.
+The `jitsi.matrix.<your-domain>` subdomain may be necessary, because this playbook could install the [Jitsi video-conferencing platform](https://jitsi.org/) for you. Jitsi installation is disabled by default, because it may be heavy and is not a core required component. To learn how to install it, see our [Jitsi](configuring-playbook-jitsi.md) guide. If you do not wish to set up Jitsi, feel free to skip the `jitsi.<your-domain>` DNS record.
 
 
 ## `_matrix-identity._tcp` SRV record setup