[feature] Allow several subnets to have the same subnet address (for private ip addresses)

[okraits]

Subnets within private ip address ranges (https://en.wikipedia.org/wiki/Private_network#Private_IPv4_addresses) are used for private, local ip addresses.
Thus, several devices can use the same subnets in those address ranges at the same time.
Currently OpenWISP IPAM doesn't allow subnets to have the same subnet address.

It should be possible to create several subnet objects with the same subnet address.
One possibility would be to introduce the subnet types public and private. public subnets need to have unique subnet addresses, private subnets don't.

[pandafy]

@okraits can you provide examples of the conflicting subnets?

If I recall correctly, the module allows to create overlapping subnets in different organizations.

[nemesifier]

@okraits I am not aware of anyone using this module to manage public ip addresses.

The main purpose of this module is to allow automatic management of the address space (eg: create new IP addresses and subnets, divide subnets into smaller subnets, automatically assigning an IP based on the first available address) while avoiding conflicts and overlap.

It's meant to be used when the address space is shared in a single organization and conflicts are undesired.

So what's the use case for this feature request?

Right now, if you have different network resources using the same subnet but you still care about using this module, you can either:

• Keep the same address space but use different organizations
• Use different private subnets instead of using the same one

If we want to allow different network resources to use the same subnets within a single organization while keeping the conflict/overlap avoidance features then we need to introduce another concept into the mix, something like "Address space", so an organization can have multiple address spaces and choose which one they want to use for each IPAM related operation, then we'd need to change OpenWISP Controller too to make it aware of this new address space thing, sounds like a lot of work and an amount of corner cases to handle which is hard to predict.