Monitoring performance on Ethernet interfaces comes down to monitoring bandwidth utilization using the methods described in Chapter 12, "Monitoring System Interfaces."
MIB Variables for Ethernet Traffic
The following MIB objects (from RFC 2233) are the most useful in measuring the amount of traffic flowing across Ethernet interfaces:
From RFC 1757, the etherStatsOctets object provides a count of input and output octets summed together.
From MIB RFC 1213, the sysUpTime object provides the number of time ticks counted since the device was initialized. This object must be sampled on each poll to determine whether the interface counters rolled over.
From MIB CISCO-STACK-MIB, the sysClearMacTime and sysClearPortTime objects provide the number of time ticks since the counters were cleared. On Catalyst switches, these objects must be sampled on each poll for Catalyst switches to determine whether the counters were cleared.
The separate input and output counters from the ifTable must be used for full-duplex interfaces. The single counter from the etherStats table is handy for half-duplex interfaces because it already sums the counts together.
The high-capacity counters are necessary to measure traffic on Gigabit Ethernet interfaces. Otherwise, you must poll the device too frequently to make sure you do not miss the counter rolling over.