Users Guide

900 Port-Based Traffic Control
What is Flow Control?
IEEE 802.3 Annex 31B flow control allows nodes that transmit at slower
speeds to communicate with higher speed switches by requesting that the
higher speed switch refrain from sending packets. Transmissions are
temporarily halted to prevent buffer overflows. Enabling the flow control
feature allows Dell EMC Networking N-Series switches to process pause
frames received from connected devices. Dell EMC Networking N-Series
switches do not transmit pause frames.
Flow control is supported only on ports that are configured for full-duplex
mode of operation.
What is Storm Control?
A LAN storm is the result of an excessive number of broadcast, multicast, or
unknown unicast messages simultaneously transmitted across a network by a
single port. Forwarded message responses can overload network resources and
cause network congestion.
The storm control feature allows the switch to measure the incoming
broadcast, multicast, and/or unknown unicast packet rate per port and discard
packets when the rate exceeds the defined threshold. Optionally, the system
can issue a log message and a trap, or it can shut down (diagnostically disable)
the port. Storm control is enabled per interface, by defining the packet type
and the rate at which the packets are transmitted. For each type of traffic
(broadcast, multicast, or unknown unicast) a threshold level can be
configured, which is expressed as a percentage of the total available
bandwidth on the port. If the ingress rate of that type of packet is greater than
the configured threshold level the port drops the excess traffic until the
ingress rate for the packet type falls below the threshold.
When configuring the limit in terms of link bandwidth, the actual rate of
ingress traffic required to activate storm-control is based on the size of
incoming packets, and a hard-coded average packet size of 512 bytes is used
to calculate a packet-per-second (pps) rate, as the forwarding-plane requires
LLPF Filters proprietary protocols that should not normally be relayed
by a bridge.
Table 23-1. Port-Based Traffic Control Features
Feature Description