[j-nsp] MX960 with 3 RE's?

[Saku Ytti]

On 15 January 2016 at 01:39, Christopher E. Brown
<chris.brown at acsalaska.net> wrote:
> The 30Gbit nominal (actual 31.7 or greater) limit per trio applies to the MPC1 and 2 cards
> but the quad trio interconnect in the 16XGE is wired up diff with additional helpers and
> can do the full 40G per bank.


Pretty sure this is not true. There are three factors in play

a) memory bandwidth of trio (mq)
b) lookup performance of trio (lu)
c) fabric capacity

With SCBE 16XGE isn't limited by fabric, but it's still limited by
memory bandwidth and lookup performance.

Memory bandwidth is tricksy, due to how packets are split into cells,
if you have unlucky packet sizes, you're wasting memory bandwidth
sending padding, and can end up having maybe even that 30Gbps
performance, perhaps even less.
If you have lucky packet sizes, and you can do 40Gbps. For me, I work
with half-duplex performance of 70Gbps, and that's been safe bet for
me, in real environments.

Then there is lookup performance, which is like 50-55Mpps, out of
60Mpps of maximum possible.



Why DPCE=>MPC is particularly bad, is because even though MQ could
accept 20Gbps+20Gbps from the fabrics DPCE is sending, it's not, it's
only accepting 13+13, but DPCE isn't using the last fabric to send the
remaining 13Gbps.
So if your traffic flow from single DPCE card (say 4x10GE LACP) is out
to single trio, you'll be limited to just 26Gbps out of 40Gbps.

If your chassis is SCBE or just MPC1/MPC2 you can 'set chassis fabric
chassis redundancy-mode redundant', which causes MPC to use only two
of the fabrics, in which case it'll accept 20+20 from DPCE, allowing
you to get that full 40Gbps from DPCE.
But this also means, if you also have 16XGE and SCB, you can pretty
much use just half of the ports of 16XGE.

If this is confusing, just don't run mixed box, or buy SCBE and run
redundant-mode.



-- 
  ++ytti