[smokeping-users] fping reporting extreemly high packet loss when a standard ping doesn't

[Kevin and Leah Branch]

Hi, 
I'm new to SmokePing, and very impressed with its functionality and ease of use.  I've already set up link quality tracking to many of the sites in my enterprise, and I'm very pleased with it.

I have one site that is a couple of satelite hops and a microwave link away that normally has very high ping latency.  When I run a standard Windows or Linux ping of that site, I get very little or no packet loss, though the expected high latency.  When I run fping against it, I get tons of packet loss reported.  This appears to be why SmokePing is continuously reporting more than 50% packet loss to that site, though I know that's not accurate.
  [root at linux-dev probes]# fping X.X.X.X -C10
  X.X.X.X : [0], 84 bytes, 1412 ms (1412 avg, 50% loss)
  X.X.X.X : [2], 84 bytes, 1106 ms (1259 avg, 50% loss)
  X.X.X.X : [4], 84 bytes, 1196 ms (1238 avg, 50% loss)
  X.X.X.X : [6], 84 bytes, 1466 ms (1295 avg, 50% loss)
  X.X.X.X : [8], 84 bytes, 1124 ms (1261 avg, 50% loss)
  X.X.X.X : 1412.98 - 1106.73 - 1196.79 - 1466.00 - 1124.52 -
Experimentally I told fping to space its ping attempts at 5 second rather than the default 1 second interval, and the false packet loss disappeared.
  [root at linux-dev probes]# fping X.X.X.X -C10 -p5000
  X.X.X.X : [0], 84 bytes, 1979 ms (1979 avg, 0% loss)
  X.X.X.X : [1], 84 bytes, 2640 ms (2310 avg, 0% loss)
  X.X.X.X : [2], 84 bytes, 2105 ms (2241 avg, 0% loss)
  X.X.X.X : [3], 84 bytes, 3625 ms (2587 avg, 0% loss)
  X.X.X.X : [4], 84 bytes, 2748 ms (2619 avg, 0% loss)
  X.X.X.X : [5], 84 bytes, 3180 ms (2713 avg, 0% loss)
  X.X.X.X : [6], 84 bytes, 3492 ms (2824 avg, 0% loss)
  X.X.X.X : [7], 84 bytes, 3776 ms (2943 avg, 0% loss)
  X.X.X.X : [8], 84 bytes, 2931 ms (2942 avg, 0% loss)
  X.X.X.X : 1979.61 2640.79 2105.45 3625.81 2748.30 3180.89 3492.70 3776.15 2931.10 -
It looks like if one ping takes longer than the fping interval to get back, that it causes the next ping to be reported lost for some reason.  

However, even with a high -p value, I am ALWAYS getting the last ping reported as lost.  What in the world?

I don't know why this is happening, but it appears I can remedy this by forcing the fping interval to 5000ms.  But how do I configure the SmokePing Fping probe to do this when the only documented fping paramater the the probe supports appears to be packetsize?  Should I monkey around with lib/probes/FPing.pm?  I tried that but all by graphing died.  Is there a cleaner way?  

Maybe there is a better solution to getting accurate packet loss reported for sites that regularly have more than 1000ms of latency.  I welcome anyone's suggestions.

Thanks!
Kevin



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