Deployment Guide

Restore Queue Drop State
You can restore the queue drop triggered due to the storm control PFC detection to the normal state.
Once the storm control PFC is detected on a port or priority, you can activate the queue drop action. You can restore the
dropped queue to normal state on the following conditions.
● You can restore the queue after a particular period of time. Use the queue-drop backoff-force polling—count
command to remove the queue-drop state after the specified number of polling is done. The queue-drop state, which has
been activated due to the detection of storm control PFC, is forced to get removed. When the number of polling-interval
is set as ‘zero’, the queue-drop state is not removed until it is explicitly cleared using the storm-control pfc in
queue-drop-state clear command.
● You can restore the queue when additional PFC packets for a particular priority are not received for a specified period
of time. Use the queue-drop backoff-on-norxpfc polling-count command to remove the queue-drop state if
additional PFCs are not received after the specified number of polling is done.
For more information about the above commands, see the Dell EMC Networking OS Command Line Reference Guide.
PFC Storm
When packets flood a network, the result is excessive traffic which affects the performance of the network. When Priority Flow
Control (PFC) is enabled on a port, the traffic flows according to the priority of the data.
Limitation: Dell EMC Networking OS does not support storm-control pfc, when the policy map uses trust diffserv for
packet classification.
PFC storm is the inconsistencies found in the traffic that flows through a PFC enabled port. You can detect this by polling the
lossless queues on each port. This polling is done at periodic intervals. If the queue has traffic with the corresponding egress
counter not getting incremented, then the condition is detected as PFC storm. During such conditions, the traffic corresponding
to the port or priority can be dropped for a specific period of time to overcome the degrade in the network performance.
Once you detect PFC storm on a port or priority, you can discard all packets on that port/priority and enable drop of the queue,
so that traffic corresponding to other priorities is not affected. You can restore the dropped queue to normal state after a
period of time.
View Details of Storm Control PFC
You can view the status of storm control PFC and the statistical details by using the following Show commands.
Use the show storm-control pfc status stack-unit unit-number port—set portpipe-number command
to view the status of the storm control PFC on a specified stack unit. The following example shows the status on stack unit 0
with port set 0.
DellEMC#show storm-control pfc status stack-unit 1 port-set 0
-------------------------------------------------------------------------------------------------------
Interface Priority State Duration in discard state(in ms) Pkts Dropped(Ingress) Pkts Dropped(Egress) Pkts
Dropped(Ingress,Cumulative) Pkts
Dropped(Egress,Cumulative)--------------------------------------------------------------------------------------------------
-----
Fo 1/32/1 4 Drop 1194740 2389 135759218588
2389 135759218588
Fo 1/1/1 4 Normal 0 0 0
0 0
Fo 1/17/1 4 Normal 0 0 0
0 0
Use the show storm-control pfc statistics stack-unit unit-number port—set portpipe-number
command to view the statistical data of the storm control PFC on a specified stack unit. The following example shows the
statistics on stack unit 0 with port set 0.
DellEMC#show storm-control pfc statistics stack-unit 0 port—set 0
--------------------------------------------------------------------------------
Interface Priority Discard State Count Discard State Clear Count
forced No rxPfc
--------------------------------------------------------------------------------
Te 0/0 3 2 0 0
4 2 0 0
Storm Control
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