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Background: Know: INTEGER, Recognize: 

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Defined Types: Counters and Gauges. This page discusses two basic types of objects: counters and gauges. They can be used by MRTG (Multi Router Traffic Grapher) to monior the traffic load on network-links.

COUNTERS

A counter is an object that returns an unsigned integer that grows over time. It has the following characteristics.

–non-negative.

–monotonically increasing.

–wrap around.

For example:

It can be used to track the TCP connections. The number in the counter will increase by 1 every time a new connection is established. This number is always incrementing. MRTG will poll a configured counter every 5 minutes, subtract the last number it got, and divides it by the number of seconds in 5 minutes. This gives us the number of new TCP connections per second in the 5 minutes. It can be seen from the following figure:

10:10am:  123394 connections 
10:15am:  138854 connections

138854 - 123394 = 15460 connections in the past 5 minutes

15460 connections / 300 seconds (in 5 minutes) = 52 connections per second
(rounded)

GAUGES:

A gauge is a different type of variable. A gauge integer will go up an down according the variable it tracks. It has the following characteristics:

–non-negative

–increase or decrease

–capped at extremes

For instance, concurrent TCP sessions on a given device can be considered as a gauge. MRTG just takes the number polled and graphs that number, without math done.

COUNTERS vs GAUGES

Counters and gauges are good for measure different types of metrics. However, concurrent sessions can only be measured by a gauge. It tells how many active TCP sessions there are at a specific moment in time. Bandwidthe is best measured by a counter. Every time a bit passes an interface, the interface counter is incremented.

Simply speaking, any item that we need in something per second, we need to have a counter. If we just need a variable graphed, then we need a gauge.

See also

TELE9752 lecture slide

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