[j-nsp] ex4500 best-effort drops nowhere near congested

[Jeff Wheeler]

On Wed, May 1, 2013 at 8:27 PM, ryanL <ryan.landry at gmail.com> wrote:
> i'm guessing this is a buffer thing, but i can't explain why it only
> happens on my 1ge ports and not when i punt the traffic over an 10ge

Yes, it is a buffer thing.  A 10GE interface is basically never going
to not have time to transmit frames unless it is receiving from 10 or
more 1GE interfaces at the same instant, steadily, for long enough to
fill the buffer; or there is at least one 10GE interface also talking
to it.  On the other hand, two 1GE interfaces transmitting toward the
same out-going 1GE port can fill its buffer.

This is sometimes not obvious, because you look at the long-term
traffic and see a few hundred Mb/s, thinking, "why is there packet
loss?"  You must keep in mind that the available buffer on modern ToR
switches is often less than 1ms worth of traffic.

The "buffer bloat" discussion of recent years has not done us any
favors.  Many customers now think that buffers have historically been
too big.  In fact, they were just often used incorrectly / configured
badly.  Now we are not evaluating purchases based on having sufficient
buffer, so vendors have spent years developing products that ... lack
sufficient buffer.

-- 
Jeff S Wheeler <jsw at inconcepts.biz>
Sr Network Operator  /  Innovative Network Concepts