Now CLOS design is not fundamentally new, but most of the Network Engineers were not talking about it till recent times (Well...this is true to an extent). So as Network Engineer should you really care ?
Well you should start by asking why CLOS in first place ?
The major problem that CLOS fabric solves is about solving scalability issues. While scalability is a matter of context, it's not necessary that everyone needs or to be precise going too far about it.
Also CLOS fabric also doesn't define your Layer2 - Layer 3 boundaries itself. So you are pretty much dependent upon what works best for you from vendor implementation perspective while keeping your overall goal in mind. Now in theory Layer 3 Fabrics scale much better than Layer 2 Fabric. Here are some questions/Things you figure out about CLOS if you decide to go for it :
- What is the scale that you got to deal with ?
- What are technical and business requirements ?
- Your DC traffic is mostly east-west or north-south ?
- How you can minimize the state of the Core (Spine) to minimum ?
- How flooding works in your fabric ?
- How multicast is handled in fabric ?
- Where to define Layer2-Layer 3 boundary ?
- Your network is going to multi vendor now/In future ?
- How you gonna manage and monitor such large network ?
- How you gonna introduce security & Services such as Load Balancer ?
- How you gonna connect to external world ? (Border Spine Vs. Border Leaf)
- Define you convergence requirements
- You gonna need single or multi stage CLOS ?
- Your over subscription ratio ? (Usually 3:1 is good for most part)
- Understand your failure domains and impact they may have
- Do you need Spine to Spine or Leaf to Leaf connections to mitigate some of
failure scenario ?
- If you are going with Layer 3 fabric, is it going to be good idea to use
- EBGP vs IBGP (Also RR placement) in Layer 3 fabric ?
Even as an example, Cisco's famous buzzword these days ACI (Application Centric Infrastructure ) also uses Spine & Leaf design. It uses
Cisco ACI is kind of build around another buzz word that you hear more often these days called SDN (Software Defined Networks). Now whether it fits into true SDN definition or not needs another discussion :).
In the mean while below is the list of URLs which you may find very handy to get started with CLOS: