Slow 40G->10G Performance when Traffic Flows over MLAG IPL

Hi,

I have a pair of SX1410’s configured with MLAG. In a situation where a 40G port is trying to send traffic to a 10G port located on the partner switch, the performance is terrible - in this case around 50-60Mbps. Where receiving, the 40G attached host receives from the 10G host at nearly line speed (9.9Gb/s)

When the same 40G port sends traffic to a 10G port located on the same switch, the performance is very good, nearly line speed (9.9Gb/s).

There is no other traffic currently on the switches and I am using iperf to test, but can reproduce with other applications. Flow control is enabled pretty much every, so maybe this has a bearing. I cannot reproduce the problem where hosts are both 40G in any combination of tests - that works absolutely fine.

Any ideas?

Regards,

Barry

Hi,

The issue has been resolved via support. The config was missing the following:

interface port-channel 1 vlan map-priority 0 traffic-class 1

dcb priority-flow-control priority 0 enable

It may be worth updating the community MLAG how-to’s with these lines as I don’t believe this is in there.

With that in, everything is now working well.

Great - thanks for the update.

Hi, Can you attach a basic topology diagram, showing the ports with the performance problem, and how they are connected?

Are the inter-switch ports showing any discards or errors?

Are the inter-switch ports part of a port channel? Is there mlag configured on these inter-switch ports?

You wrote:

“When the same 40G port sends traffic to a 10G port located on the same switch, the performance is very good, nearly line speed (9.9Gb/s).”

Did you do this same test on “both” switches?