Spine-Leaf Switch Topology

Hi,

I've started to look more into the whole spine-leaf topology topic but I'm not sure I really get it on a deeper technical level. The most confusing aspect stems from all the "No STP" talk.

For the sake of simplicity let's just say I have one server, two leaf switches and two spine switches. So now I connect both NICs of the server with both leaf switches and both leaf switches with both spine switches. Neither spine nor leaf switches are directly connected to each other. (Leaf - Leaf or Spine - Spine)

So far so good. What's confusing me the most is all this talk about implenting this via L3 or L2. Does Layer 3 implementation mean that every uplink from Leaf to Spine has it's own network? For example:

- Leaf1 Port1 10.0.0.1/24 to Spine1 Port1 10.0.0.2/24
- Leaf1 Port2 10.0.1.1/24 to Spine2 Port1 10.0.1.2/24
- Leaf2 Port1 10.0.2.1/24 to Spine1 Port2 10.0.2.2/24
- Leaf2 Port2 10.0.3.1/24 to Spine2 Port2 10.0.3.2/24

So no need for STP since broadcasts won't cross into different networks = No switching loops?

And even more confusing to me is the Layer 2 implementation. If every Leaf Switch is connected with every Spine Switch, how are loops prevented? I've read about SPB / TRILL - Is this just used as better alternative to STP?

If so - Would that mean that for example Ubiquiti devices (EdgeSwitch) cannot be used for Spine-Leaf topology since (as far as I know) they do not support SBP / Trill on Layer 2 and also only have minimal L3 support so a L3 implementation is also off the table?

Thanks!