The term “Storm” in Networking refers to packets flooding a specific broadcast domain which ultimately results in poor network performance. Cisco came up with a solution to mitigate such detrimental scenarios and it’s called “Storm Control” sometimes referred to as “Traffic Suppression”. As the name implies, it basically monitors incoming traffic levels every second and compare it with a hard-coded storm control level which is typically a threshold on a given interface that sets a limit in terms of
the number of packets of different type. The traffic storm control level is a percentage of the total available bandwidth of the port. Each port has a single traffic storm control level that is used for all types of traffic (broadcast, multicast, and unicast).

Let’s get on the console and configure it…

Note here that the we have different options with the “storm-control” command at the interface level. Here, we can enable either broadcast, multicast or unicast traffic storm control on the interface and also set an action if a storm is detected. Note that the default is “Drop”. Let’s chose the “broadcast” option and see what we have…

Notice here how we can specify a threshold based on different measures; bites per sec, packets per sec or even by percentage on the interface bandwidth (rising threshold).

Let’s configure a threshold of 45% of the interface bandwidth for broadcast traffic…

Let’s configure threshold for both Multicast (bps) and Unicast (pps) traffic…

Notice here that we can set a value in either Kbps, Mbps or Gbps. We did set it to 20Mbps. Let’s set a threshold for Unicast traffic…

So here, we set the the maximum threshold to 25Mbps and the falling threshold to 15Mbps which means traffic exceeding 25Mbps will be dropped and we will only permit it again if traffic is lower than 15Mbps.

Note that we also have the capability to set different action in case of a storm. Let’s see those options…

Here, we can shutdown the interface or send an SNMP trap in case of a storm. Let’s run a few verification commands…

That completes this topic. Please let me know if you have any questions.