Sorry, I have messed up with the names.
I will try to guide you through Horizon.
Project -> Network -> Routers: Create router set name to 'test', leave empty 'External network'
Go to your new router:
Project -> Network -> Routers -> test: - switch to "Interfaces" tab - click "Add Interface"
Select Subnet (choose your external one), leave IP Address empty. Submit and check what IP you got.
Sorry, I have messed up with the names.
I will try to guide you through Horizon.
Project -> Network -> Routers: Create router
set name to 'test', leave empty 'External network'
Go to your new router:
Project -> Network -> Routers -> test:
- switch to "Interfaces" tab
- click "Add Interface"
Select Subnet (choose your external one), leave IP Address empty.
Submit and check what IP you got.