[c-nsp] Reliability? (hopefully trivial question)

[Bruce Pinsky]

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Jeff Kell wrote:
> How exactly (or approximately will do) does IOS calculate interface "reliability"?  I'm looking at a pretty crappy link now that shows:
> 
> 
>>  MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,
>>     reliability 159/255, txload 1/255, rxload 1/255
> 
> 
> I'm thinking some function of errors/packets (%error) then...?  input and output combined?  last five minutes like load?  Based on actual data packets?  keepalives?  BPDUs?
> 


Yes, it is a function of errors divided by number of frames.  And it is
decayed.

Goes a bit like this:

IntervalFrames = Received in interval + Transmitted in interval
IntervalErrors = RX errors in interval + TX errors in interval


IntervalReliability = 255 * ((255 * IntervalErrors) / IntervalFrames)
where IntervalReliability is always >=128

OngoingReliability = IntervalReliability + (((OngoingRealability -
IntervalReliability) * DecayFactor) / 1000)


There is a slightly different calculation if the interface has LAPB
encapsulation (i.e. X25).

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bep

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