Performance management of system interfaces really boils down to monitoring bandwidth utilization, which means counting the octets that flow across a given interface and measuring those counts against the bandwidth of the interface. This way, you can determine whether you are overutilizing a particular link and when you need to increase the capacity of a link. In Chapter 4, “Performance Measurement and Reporting,” we discussed the method for calculating link utilization:
Calculating the delta (difference) between two collections of ifInOctets and ifOutOctets each.
Adding the deltas together.
Converting the combined value to bits per seconds (× 8 / (num of seconds in Δ)).
Dividing the bits by ifSpeed (interface ...