Friday, November 15, 2013

Cisco Nexus 3548 - Configuring Active Buffer Monitoring

It never ceases to amaze me that people value time as money. To me time is more than money. I can make money and I can make more if I worked at it, but time -- that's a different story. I cannot make time, I cannot buy more time, I cannot take it from someone else -- Once it's gone it's gone forever. As I sit here on the train (my daily hour commute) the time it's taking me to write this blogtorial is gone. I can never get it back so hopefully I am doing something worthwhile, something that will help someone, and something that I enjoy. With all that aside let's go into how to configure 'Active Buffer Monitoring' on a Cisco Nexus 3548.

When you are down to nanoseconds on port to port latency, monitoring your buffer space becomes more crucial than ever. Because whenever you buffer your switch is now store and forward for those buffered bytes instead of cut through. If you're switch is store and forward then you are not getting the ~ 230 nanoseconds port-to-port latency that you just spent $20K for.

Before we can dive into configuring buffer monitoring it would be beneficial to understand buffer blocks and how the ports are mapped. First there are 3 buffer blocks each containing 6MB worth of buffer space which gives us a total of 18MB shared buffer. Ports to these buffer blocks (3 x 6MB) are mapped as follows.