Understanding Rate Limiting; Using Rate Limiting To Control Packet Storms - Symbol ES3000 Manual

11-2 ES3000 Advanced Concept Guide

11.1 Understanding Rate Limiting

Rate limiting, or storm control, prevents ports on the ES3000 switch from being overwhelmed by a
DLF, broadcast, or multicast packet storm.
DLF is an abbreviation for Destination Lookup Failure. When a Level 2 Ethernet switch receives a
packet for a MAC address which is not yet known to be reachable through particular port, the packet
is copied or flooded to all of the ports on the switch (or VLAN).
A storm results when packets overwhelm the LAN, which degrading network performance.
With rate limiting enabled, the switch monitors incoming traffic and counting broadcast packets,
multicast packets, and packets for which there has been a destination lookup failure. The switch
keeps a separate count of the packets for each type of traffic. When traffic for any one type reaches
the threshold, the switch suppresses further traffic of that type until traffic of that type falls below
the threshold.
With rate limiting disabled, all traffic is allowed.

11.2 Using Rate Limiting to Control Packet Storms

Use the Storm Control Configuration page (QoS > Rate Limiting > Broadcast Storm Control) to enable
or disable the different types of storm control and set the packet count threshold.
In the web interface, the administrator can set storm control parameters globally, to apply to all ports.
To configure storm control on a port-by-port basis, use the command-line interface.
This page displays the following:
• DLF: Unicast (DLF) storm control enabled or disabled. Click the check box for DLF, select
Enabled or Disabled from the drop-down list, then click Apply.
• Broadcast: Broadcast storm control enabled or disabled. Click the check box for Broadcast,
select Enabled or Disabled from the drop-down list, then click Apply.
• Multicast: Multicast storm control enabled or disabled. Click the check box for Multicast,
select Enabled or Disabled from the drop-down list, then click Apply.
• Threshold: The number of packets allowed per second before rate limiting applies. This
threshold value applies to all three types of storm control, broadcast, multicast and DLF,
though it applies to each seperately. A threshold of 4000 packets per second would allow
3999 broadcast packets a second, 3999 multicast packets a second, and 3999 DLF-handled
packets a second without triggering any traffic supression.