We've been trying to track down why our 5100's are dropping traffic due
to lack of buffer space, even with very low link utilization.
It seems like they're classifying all our traffic as best-effort:
> show interfaces xe-0/0/49:0 extensive
....
Carrier transitions: 1, Errors: 0, Drops: 276796488, Collisions: 0,
Aged packets: 0, FIFO errors: 0, HS link CRC errors: 0, MTU errors: 0,
Resource errors: 0, Bucket drops: 0
Egress queues: 12 supported, 5 in use
Queue counters: Queued packets Transmitted packets Dropped packets
0 0 1876090180637 276796488
3 0 0 0
4 0 0 0
7 0 663877 0
8 0 0 0
Then, if we look at those queues:
> show class-of-service forwarding-class
Forwarding class ID Queue Policing priority
No-Loss
best-effort 0 0 normal Disabled
fcoe 1 3 normal Enabled
no-loss 2 4 normal Enabled
network-control 3 7 normal Disabled
mcast 8 8 normal Disabled
So whatever, we've got queues configured for traffic we never see.
That's not really a huge deal. But then:
> show class-of-service shared-buffer egress
Egress:
Total Buffer : 12480.00 KB
Dedicated Buffer : 3744.00 KB
Shared Buffer : 8736.00 KB
Lossless : 4368.00 KB
Multicast : 1659.84 KB
Lossy : 2708.16 KB
To me, this appears that the 5100's by default reserve about 70% of the
available shared port buffers for lossless+multicast traffic. The
documentation seems to back me up here:
https://www.juniper.net/documentation/en_US/junos/topics/concept/cos-qfx-series-buffer-configuration-understanding.html#jd0e1441
https://www.juniper.net/documentation/en_US/junos/topics/example/cos-shared-buffer-allocation-lossy-ucast-qfx-series-configuring.html
Has anyone else encountered this? We're going to be adjusting the
buffers per the documentation, but I'd be really interested to hear if
anyone has hit this before.
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