[c-nsp] Temporal buffer calculations on ASR9K

John Neiberger jneiberger at gmail.com
Fri Feb 28 21:44:27 EST 2014

I just want to get a sanity check on some WRED settings. This is a 100G
linecard. If I have a class with "bandwidth remaining percent 1"
configured, as well as random detect 10ms 20ms configured, I believe that
means that WRED kicks in when the allotted buffer space is 10 ms full. If
I'm reading the docs right, that means we calculate the buffer minimum
value by multiplying 0.010s * 1Gbps / 8, for a minimum buffer value of 1.25
MB. The docs say that value gets rounded up to 1.536 MB, so WRED kicks in
when the link is congested and the buffer has filled to at least 1.536 MB
and will do 100% taildrop when it fills to twice that value (20ms).

Is that about right or am I off base?


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