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

[Benny Amorsen]

joel jaeggli <joelja at bogus.com> writes:

> There's literally no options in between. so a 1/10Gb/s TOR like the
> force10 s60 might have 2GB of shared packet buffer, while an like an
> arista 7050s-64 would have 9MB for all the ports, assuming you run it
> as all 10Gb/s rather than 100/1000/10000/40000 mixes of ports it can
> cut-through-forward to every port which goes a long way toward
> ameliorating your exposure to shallow buffers.

Why does cut-through help so much? In theory it should save precisely
one packets worth of memory, i.e. around 9kB per port. 500kB extra
buffer for the whole 50-port switch does not seem like a lot.

Lots of people say that cut-through helps prevents packet loss due to
lack of buffer, so something more complicated must be happening.


/Benny