LAB 3.1 Task 5: Log into the new instances ( Nova Networking)

Note : this is not a problem report for lab 3.1 but rather a general question.

Instead of launching the lab environment for the Lab 3.1, I decided to continue my work from the Launched lab environment from Lab 2.1 and noticed that once it gets to this section, when I try to launch a new instance, it will not receive any IP address because I removed the following lines from local.conf before running the stack.sh script.

#FIXED_RANGE=10.10.128.0/20 #Range for private IPs

#FLOATING_RANGE=192.168.100.128/25 #Range for public IPs

Now i'm trying to figure out how to allocate that IP address manually and can't find any option to that and wondering if I'm simply missing an option somewhere or it is not possible...

Also, I'm having a hard time to understand what is happening in here; for example, in VMware or KVM environment, as far as I know, we never need to assign fixed or floating range anywhere, you simply allocate an IP to your host and afterward you can launch as many VMs with whatever IP you want. of course, if you want those IPs to work, we have to configure the virtual and physical switches and perform other Network tasks to make the routable.so... what is the purpose of Fixed and Floating range?

The other question is that why is  it that Neutron networking no longer needs these parameters?