There's no good answer to this. It will vary wildly depending on the organization, what type of work they do, what applications they use and their users. If I'm building something today I'd use at least 10 Gbit/s to connect layers unless I know traffic will be very low and price is the most important factor.
What leaf and spine gives you is consistent performance and latency and to be able to forward on all links, if you have built a layer three topology.
We can't make blanket statements like it will lower TCO. TCO is something you have to calculate.
@deniel thanks for reply. I can agree on access layer with 10 Gbps uplink because it's port subscription will go up to 2.4 or 4.8 and it's is acceptable. Now my question is for the Distribution layer and server farm switching. Here, a High cost is involved in the core and distribution layer ports. Each port is increasing TCO.
Here, you suppose that I have 20 access layer switches and now I am connecting all access layer to distribution and distribution to core layer. Here if I will connect two uplinks between distribution and core then port over subscription will be 10 or higher. Is it acceptable?
sorry but I am adding another question about migration core and distribution layer in a single layer means remove thr core layer and let handle all core layer functions to the distribution layer switching ( off course need some higher switch), it will help us to maintain budget then what will prons and cons in administrative and reliability of the network?
This forum is for learning and certifications, not for doing free consultancy. Leaf and spine is mainly used in DC environments but it can be used in campus environments as well. Cisco is for example pushing SDA.
Here is an example of 3-stage CLOS:
If you have 10G from distribution to access then I would have at least 40G from distribution to core.
If you need a Dist layer or not depends on port density and cost in core device, physical layout of your site, fiber connectivity and so on.
Sorry that you got my point as your free consultancy. This is not for this. Actually, I wants to know that why 3 tier design is best for enterprise network and why will not play with cisco standard (if needed).
Sorry again and thanks.
If you feeling that I am taking your free consultancy services then you can delete your reply or not to reply.
No worries, Deepak.
There is never one best design. It depends on requirements and constraints. You don't have to do a 3-tier if there is only a small access layer. You can collapse distribution and core into what is known as collapsed core. In some cases it's just a single switch or single switch stack providing both access and core services.