What Is Storm Control; What Are Protected Ports - Dell PowerEdge M420 Configuration Manual

Dell powerconnect m8024-k user's configuration guide

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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. 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) you can configure a threshold level, 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.

The actual rate of ingress traffic required to activate storm-control is based on

the size of incoming packets and the hard-coded average packet size of 512

bytes - used to calculate a packet-per-second (pps) rate - as the forwarding-

plane requires PPS versus an absolute rate Kbps. For example, if the

configured limit is 10%, this is converted to ~25000 PPS, and this PPS limit

is set in the hardware. You get the approximate desired output when 512 bytes

packets are used.

The switch supports up to three separate groups of protected ports. Traffic

can flow between protected ports belonging to different groups, but not

within the same group.

A port can belong to only one protected port group. You must remove an

interface from one group before adding it to another group.

Port protection occurs within a single switch. Protected port configuration

does not affect traffic between ports on two different switches. No traffic

forwarding is possible between two protected ports.

Configuring Port-Based Traffic Control