Understanding Storm Control
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 action-shutdown statement
or the port-error-disable statement) when the storm control level is exceeded.
To recognize a storm, you must be able to identify when traffic has reached an abnormal level. Suspect a storm when operations begin timing out and network response times slow down. Users might be unable to access expected services. Monitor the percentage of broadcast and unknown unicast traffic in the network when it is operating normally. This data can then be used as a benchmark to determine when traffic levels are too high. You can then configure storm control to set the level at which you want to drop broadcast and unknown unicast traffic.
The Junos OS allows you to configure a storm control value that exceeds the bandwidth of the interface. If you configure an interface this way, storm control does not drop broadcast or unknown unicast packets even if they consume all the available bandwidth.
Storm control is enabled by default on ELS platforms and disabled
by default on non-ELS platforms. If storm control is enabled, the
default level is 80 percent of the available bandwidth for ingress
traffic. You can change the storm control level by configuring it
as a specific bandwidth value. (The level configuration statement, which allows you to configure
the storm control level as a percentage of the combined broadcast
and unknown unicast streams, is deprecated and might be removed from
future releases. We recommend that you phase out its use and replace
it with the bandwidth statement.)
You can customize the storm control level for a specific interface by explicitly configuring either bandwidth or level (but not both at the same time for the same interface).
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.
When you configure storm control bandwidth or 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 bandwidth 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.
The sending and receiving of 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.
You can change the storm control level for a specific interface by configuring the bandwidth value or the storm control level for the combined traffic streams that are subject to storm control on that interface. The type of traffic stream (broadcast, unknown unicast, and multicast) that is included within the bandwidth or storm control level consideration depends on which types of traffic are enabled for storm control monitoring on that 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 (multicast MAC addresses outside this range are called unregistered multicast addresses).
On an FCoE-FC gateway, storm control must be disabled on all Ethernet interfaces that belong to an FCoE VLAN to prevent FCoE traffic from being dropped. Configuring storm control on an Ethernet interface that is included in an FCoE-FC gateway may have undesirable effects, including FCoE packet loss. After disabling storm control on all interfaces, enable storm control on any interfaces that are not part of an FCoE-FC gateway on which you want to use storm control. However, on an FCoE transit switch, you can enable storm control on interfaces that carry FCoE traffic.
You can enable storm control selectively for multicast traffic on a specific interface or on all interfaces.
On all switches—You can disable storm control selectively for either broadcast streams, or multicast streams, or for unknown unicast streams.
Please note the following caveats for storm control:
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On EX4300 switches, storm control triggers on registered multicast packets even if you have configured no-registered-multicast.
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On EX9200 switches, storm control is not enabled by default.
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On QFX3500 switches, when you configure storm control bandwidth, the value you configure is rounded off internally to the closest multiple of 64 Kbps, and the rounded-off value represents the bandwidth that is actually enforced. For example, if you configure a bandwidth limit of 150 Kbps, storm control enforces a bandwidth limit of 128 Kbps.
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On QFX5000 switches that run on Junos OS, the IPv4 multicast entries are classified as known entries if the route is installed in the multicast routing table in the hardware. If the destination IP address is not programmed in the hardware, the packets are classified as unknown in the hardware. Therefore, storm control works differently when no-registered-multicast knob is enabled.
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On QFX10000 switches, storm control is not supported on the Service Provider (SP) style bridge configuration.
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On a QFX10002 switch, if storm control is configured on a VLAN port associated with an IRB interface, unregistered multicast traffic is classified as registered multicast traffic if IGMP snooping is enabled. If IGMP snooping is disabled, the traffic is classified as unknown unicast traffic.
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On switches other than QFX10000 switches, storm control is applied in aggregate per port. That is, if you set a storm control level of 100 megabits and the sum of the broadcast, unknown unicast, and multicast traffic exceeds 100 megabits, storm control is initiated. On QFX10000 switches, each traffic stream is measured independently per port, and storm control is initiated only if one of the streams exceeds the storm control level. For example, if you set a storm control level of 100 megabits and the broadcast and unknown unicast streams on the port are each flowing at 80 mbps, storm control is not triggered. In this case, storm control is initiated only if one of the streams exceeds 100 mbps.
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Storm control is not enabled by default on Juniper Networks MX Series routers.
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Starting in Junos OS release 17.4R1 for MX Series routers, you can also configure storm control on logical systems.
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In implementations of storm control prior to Junos version 17.3, rate limiting ingress traffic on a given port was based on PE trap-registers wherein the ingress traffic was rate limited per traffic type. As an example, in earlier implementations on applying a storm-control profile for BUM traffic at say x%; traffic would be rate limited per stream: broadcast, unknown unicast, multicast traffic individually to x% of link bandwidth. This behavior is different from rest of Junos implementation for storm-control where the net or aggregate traffic is rate limited to x% instead of per traffic type (broadcast, unknown unicast and multicast traffic). The implementation for Junos version 17.3 and later is based on policer resource per PE chip instead of the trap-registers and is coherent with the storm-control behavior across different Junos platforms.
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