Tweaking the interface load interval

Posted by stretch in Tips and Tricks on Saturday, 21 Jun 2008 at 7:13 a.m. GMT

By default, the load for an interface is calculated over a five-minute interval. This is apparent from the output of a show interface command: 

Router# show interface f0/0
FastEthernet0/0 is up, line protocol is up
  ...
  5 minute input rate 87000 bits/sec, 17 packets/sec
  5 minute output rate 93000 bits/sec, 19 packets/sec
  ...

Of course, five minutes is an unacceptable length of time to idle while troubleshooting a critical link. Fortunately the window for statistics gathering is configurable with the load-interval command. From the IOS 12.4 documentation:

To make computations more reactive to short bursts of traffic, you can shorten the length of time over which load averages are computed.

If the load interval is set to 30 seconds, new data is used for load calculations over a 30-second period. This data is used to compute load statistics, including the input rate in bits and packets per second, the output rate in bits and packets per second, the load, and reliability.

The load interval must be between 30 and 600 seconds, specified in increments of 30 seconds. Below we shrink the load interval to 30 seconds on the interface being monitored to achieve a reading much closer to real-time: 

Router(config-if)# load-interval 30
Router(config-if)# ^Z
Router# show interface f0/0
FastEthernet0/0 is up, line protocol is up
  ...
  30 second input rate 235000 bits/sec, 26 packets/sec
  30 second output rate 242000 bits/sec, 28 packets/sec
  ...

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