We're experiencing output discards in couple of our N9K-C9372PXs. Seems like egress queues fills and it ends up in a lots of discarded packets.
All interfaces where discards occur are NEXUS interfaces (to FEX ports.)
show interface ethernet 1/21 | inc "output discard"
0 lost carrier 0 no carrier 0 babble 32043410 output discard
Bandwidth wise they're OK. I think it's due to bursty traffic from multiple uplinks (traffic comming from 6 Uplinks to 2 FEX ports). So, things like DNS queries - which're using UDP packets are really damaged by that. Could you say how to check the size of the buffer and how they're filling up ?
I'm wondering: is there are any workaround for this type of behavior ?
Now we're using:
show hardware qos ns-buffer-profile
NS Buffer Profile: Burst optimized
i see there are commands like these:
hardware qos ns-buffer-profile ultra-burst
Maybe you know, would ultra-burst mode help in our situation ? And what is requirements on entering that command ? do it requires reboot ?
or maybe it's possible to make some type of queuing where we'd treat UDP packets differently ?
also we have few older N5K-C5672UP, N5K-C5548UP and them are not experiencing it. Maybe they have 'bigger hardware' buffers ?
Thanks for any input.