Understanding Storm Control On Ex Series Switches - Juniper JUNOS OS 10.4 - FOR EX REV 1 Manual

CHAPTER 93
Rate Limiting Overview

Understanding Storm Control on EX Series Switches

Copyright © 2010, Juniper Networks, Inc.
Understanding Storm Control on EX Series Switches on page 3013
Understanding Unknown Unicast Forwarding on EX Series Switches on page 3014
A traffic storm is generated when messages are broadcast on a network and each
message prompts a receiving node to respond by broadcasting its own messages on the
network. This, in turn, prompts further responses, creating a snowball effect. The LAN is
suddenly flooded with packets, creating unnecessary traffic that leads to poor network
performance or even a complete loss of network service. Storm control enables the
switch to monitor traffic levels and to drop broadcast, multicast, and unknown unicast
packets when a specified traffic level—called the storm control level—is exceeded, thus
preventing packets from proliferating and degrading the LAN. As an alternative to having
the switch drop packets, you can configure it to shut down interfaces or temporarily
disable interfaces (see the
statement) when the storm control level is exceeded.
The factory default configuration enables storm control on all switch interfaces, with
the storm control level set to 80 percent of the combined broadcast, multicast, and
unknown unicast streams. You can change the storm control level for an interface by
specifying a bandwidth value for the combined broadcast, multicast, and unknown
unicast traffic streams. You can also selectively disable storm control on the broadcast
stream, on the multicast stream, or on the unknown unicast stream.
Broadcast, multicast, and unicast packets are part of normal LAN operation, so to
recognize a storm, you must be able to identify when traffic has reached a level that is
abnormal for your LAN. Suspect a storm when operations begin timing out and network
response times slow down. As more packets flood the LAN, network users might be
unable to access servers or e-mail.
Monitor the level of broadcast, multicast, and unknown unicast traffic in the LAN when
it is operating normally. Use this data as a benchmark to determine when traffic levels
are too high. Then configure storm control to set the level at which you want to drop
broadcast traffic, multicast traffic, unknown unicast traffic, or two or all three of those
traffic types.
statement or the
action-shutdown port-error-disable
3013