Guidance on using Medium or Large APIC cluster

[vv0bbLeS]

Hello all,

I am due to refresh one of our datacenters' APIC clusters. Currently it is a Large cluster (APIC-L2). However we have recently reduced the number of Leafs in that fabric from 24 down to 6 Leafs. There are 2 Spines in the fabric also.

With only 6 Leafs and 2 Spines left in the fabric, I was considering going with the APIC-M3 rather than the L3 for my new APIC cluster, but I haven't been able to find any guidance online as to how I should make that decision. Does it depend solely on the number of Leafs, or the number of Spines, or is it the number of endpoints, or a combination of those, or maybe something else?

[Robert Burns · Accepted solution]

If you're running less than 200 Leafs, then you'll be fine with a Medium size APICs.  Scalability found in this guide: https://www.cisco.com/c/en/us/td/docs/dcn/aci/apic/5x/verified-scalability/cisco-aci-verified-scalability-guide-521.html

Robert

[vv0bbLeS]

Ah ok excellent! I saw that document but somehow missed the table where it showed the numbers of medium and large fabrics. Thanks!

[vv0bbLeS]

@Robert Burns  I ran across something and I need a bit more guidance on this topic. I read the ACI Scalability Guide you posted above and indeed it does say that a Medium APIC cluster supports up to 200 leafs.

However, I read in this APIC Data Sheet that the APIC-CLUSTER-M3 supports "up to 1200 edge ports" which if each Leaf had 48 ports would only be 25 Leafs, not 200.

Am I reading that correctly, or how do these 2 specs reconcile? We are about to order our clusters and I want to be sure I'm not missing something here : )

[Robert Burns · Accepted solution]

The limitation is based on whichever comes first.  Up to 200 Leaf Switches (device totals) or up to 1200 [active] Leaf Interfaces.  With most typical Top of Rack (ToR) deployment switch ports are rarely max'd out.  This gives you some flexibility.  These resources are soft limits - will things fail if you have 201 switches? -  no.  1201 active ports - also no.  It's a general test & validated support limit but obviously each deployment varies with features & resource utilizations.  These limits are to ensure the best performance and that the APIC resources are sized accordingly.

Robert  

Robert

[vv0bbLeS]

Ah ok that makes sense. So I can basically read it as "up to 200 Leafs or 1200 edge ports, whichever comes first." And OK yes thanks for pointing out it's a semi-soft limitation as utilization can vary, etc! We will try to stick with what's recommended. You've cleared up my confusion! Thanks again!