[2.0a4] Provide DHCP should always allow the user to define a range in case one was already defined

[Andres Rodriguez]

I had DHCP enabled on a VLAN. I disabled DHCP with the goal of re-enable it with a different dynamic range, however, when I tried to do so I wasn't able to.

1. Disable DHCP
2. Provide DHCP -> it will only allopw you to select rack controller.

However, 2 should have showed me the dynamic range in the subnet I was wanting to use, or was already pre-defined.

[Mike Pontillo (mpontillo)]

There are some subtle issues with doing this. When you go to enable DHCP for an interface, you must have at least one dynamic range in one of the subnets associated with the VLAN.

If you have no ranges defined, the decision is easy: show the input fields for start and end IP address in the range, for convenience (so that the user doesn't have to go to the subnet details page to define the range - which by the way, we haven't implemented yet, but that's a separate issue).

If a range is already defined, we could "morph" this convenience feature into a simplistic "edit mode" which allows you to edit the range in case you made a mistake. But there some caveats to doing this:

(1) We must only allow editing if a single range is defined on a single linked subnet.
(2) If the user originally selected an incorrect subnet, there will be no way to select the correct subnet.
(3) We should continue to hide the fields if there is more than one dynamic range defined on the associated subnet(s), possibly with a warning message indicating that ranges already exist.
(4) We should make it clear to the user that they are editing an existing range and not defining a new one.

[Blake Rouse (blake-rouse)]

This will require a re-design of the dropdown. I think it would be best to use a table to show all the dynamic ranges for all subnets in the VLAN. Allow users to make all the changes they want there and then allow them to save.

But again this needs some design work and no something that fits into 2.0.