Tweaking the interface load interval

By stretch | Saturday, June 21, 2008 at 7:13 a.m. UTC

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
  ...

About the Author

Jeremy Stretch is a network engineer living in the Raleigh-Durham, North Carolina area. He is known for his blog and cheat sheets here at Packet Life. You can reach him by email or follow him on Twitter.

Posted in Tips and Tricks

Comments


david lai (guest)
December 29, 2009 at 11:56 p.m. UTC

Would making the interface load interval smaller increase processor and/or memory utilization?


alvarezp
May 6, 2010 at 5:27 p.m. UTC

I am, too, interested in David Lai's inquiry. However, at first sight it doesn't look like it would increase CPU or memory.

If I have understood correctly from the load-interval command reference, the router computes it every 5 seconds always. Load-interval will only tweak hoy many of the more recent samples will average to have a result, still every 5 seconds.

Please correct me if this is incorrect.


Praveen (guest)
January 23, 2012 at 9:14 a.m. UTC

hi Jeremy

can you explain me how can we calaculte over utilization of interface or how we know a perticular interface is over utilizing.and also explain how we check without monitoring tool that my BW is over utilizing pls explain both concept in concise way i will wait for positive notes


guest (guest)
August 13, 2013 at 8:18 a.m. UTC

If anything using a lower load-interval should decrease both memory and CPU usage, but it's likely too little to make any noticeable difference anyway.

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