Hi Gabor! This one is a really interesting question.
My first thought was simply checking the Statistics tab under the L3Out ExtEPG in the common tenant, but in your case that wouldn't provide the details you're looking for, as it aggregates the ingress/egress data without the differentation based on tenants.
Then, I thought that you could achieve it by contract logging - you could establish logging permits/denies at filter level. There's a really nice article by our colleague Soumitra here (btw, his blog is really good for all ACI-related configurations and tests, highly recommended). Unfortunately, this article mentions that logging isn't supported on a shared L3out. The article is from 2018, so I did play around with it a bit in my lab running 5.2 to see if that caveat still applies, and I managed to gather some hit counts for the traffic traversing from my EPG to an extEPG in the common tenant. Nonetheless, I didn't get any data on the amount of bits (which I'm assuming is what you'd like to bill on).
Another possible solution could be NetFlow - I was able to capture some flow records with the configuration according to the documentation on our website. I'm not sure what NMS are you running in your environment, which NetFlow versions it supports; I ran with the exporter being a barebone Ubuntu VM with flow-tools installed; I saw flow records being collected, but I didn't visualize the data or check for the specific details of packet sizes.
The simplest way to gather the information on each particular flow where I was able to filter by tenant (so you could filter flows for a particular customer) and the egress EPG (a bit more tricky, as for me the flows hitting an IP on a router were showing up with a blank EPG, so I just filtered it by "!=") was with Nexus Dashboard Insights that I have running in my lab. I'm not sure if you're utilizing it in your environment, but if so - that surely is the simplest way to set up what you're trying to achieve for billing purposes. I attached some screenshots where you can see, I got the details about the amount of packets and bytes.
I hope I was able to help out a bit and you get this to work, and please let me know if you find anything else, you got me really interested with that topic
At the same time, if anyone else at Cisco is reading this, feel free to add to what I said, I might've missed something.
Best regards,
Milosz
