Understanding Storm Control for Managing Traffic Levels
This topic uses Junos OS with support for the Enhanced Layer 2 Software (ELS) configuration style. If your switching device is an EX Series switch and runs software that does support ELS, see Using the Enhanced Layer 2 Software CLI.
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 device to monitor traffic levels and to drop broadcast, multicast, and unknown unicast packets when a specified traffic level—called the storm control level or storm control bandwidth—is exceeded, thus preventing packets from proliferating and degrading the LAN. As an alternative to having the switching device drop packets, you can configure storm control to shut down interfaces or temporarily disable interfaces (see the action-shutdown statement and the recovery-timeout statement) when the storm control level is exceeded.
On Juniper Networks EX4300 Ethernet Switches, the factory default configuration enables storm control on all Layer 2 interfaces, with the storm control level set to 80 percent of the combined broadcast, multicast, and unknown unicast traffic streams.
Storm control is not enabled by default on Juniper Networks EX9200 Ethernet Switches.
Starting in Junos OS release 17.4R1 for MX Series routers, you can also configure storm control on logical systems. Storm control is not enabled by default on Juniper Networks MX Series routers.
You can customize the storm control level for a specific interface by explicitly configuring either bandwidth level or bandwidth percentage.
Bandwidth level—Configures the storm control level as the bandwidth in kilobits per second of the applicable traffic streams on that interface.
Bandwidth percentage—Configures the storm control level as a percentage of the available bandwidth used by the combined applicable traffic streams that are subject to storm control on that interface.
You cannot configure both bandwidth level and bandwidth percentage for the same interface.
You can disable the storm control selectively for broadcast, multicast, or unknown unicast traffic, or any combination of traffic types. When disabling storm control for multicast traffic, you can specify the traffic to be either registered multicast or unregistered multicast. Registered multicast MAC addresses are multicast MAC addresses that are within the range 01-00-5E-00-00-00 through 01-00-5E-7F-FF-FF. This range has been reserved by the Internet Assigned Numbers Association (IANA) for multicast Ethernet addresses. Multicast MAC addresses that are outside this range are called unregistered multicast addresses.
The sending and receiving of broadcast, multicast, and unicast packets are part of normal LAN operation. Therefore, 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 the switching device to drop broadcast traffic, multicast traffic, unknown unicast traffic, or two or all three of those traffic types.
When you configure storm control level on an aggregated Ethernet interface, the storm control level for each member of the aggregated Ethernet interface is set to that bandwidth or level. For example, if you configure a storm control level of 15,000 Kbps on ae1, and ae1 has two members, ge-0/0/0 and ge-0/0/1, each member has a storm control level of 15,000 Kbps. Thus, the storm control level on ae1 allows a traffic rate of up to 30,000 Kbps of combined traffic streams. Traffic might include broadcast, multicast, and unknown unicast traffic, depending upon the configuration.