Install docs explains InternalURL / ExternalURL, private networks & split DNS
The externalURL is not explained on the config reference page, should probably be added there. The InternalURL is explained accurately there.
Defaults for internalURL should be added to the config reference, with our standard ports for the services. This will also mean we have defaults for this, for the first time!
The private networks/split DNS explanation could at the bottom of the 'planning and prerequesites' page in the docs.