I am just wondering a couple of things - for example if I configured storm control for lets say Broadcast and I set the rising threshold at 20% and falling to 10%.
I understand at its defaults it will drop the offending frames if I have a storm but what I’m wondering is does it still allow 20% of actual broadcast traffic through the interface while the action is in progress ?
Or does it actually block all of the broadcast traffic completely until the falling threshold is reached ?
If so how does it determine which broadcast frames to drop ?
Is it something like first in first out ?
And the second thing I was wondering is what happens to the likes of OSPF, EIGRP etc. if I have storm control for multicast configured and I get a multicast storm ?
I assume the neighbourships could be lost if the multicast traffic is blocked ?
Thanks
Concerning your first question, you’re essentially asking what algorithm is used to allow storm control to function. Well, when the rising threshold is reached, all subsequent broadcast frames are dropped completely. However, the interface is still measuring the arrival of broadcast frames and is taking into account the number of bytes that are being received even though they are being dropped.
They will continue to be dropped until the arriving frame rate falls below the falling threshold.
So to answer your question directly, it blocks all the broadcast traffic completely until the falling threshold is reached.
More details on how this algorithm works can be found in the following Cisco documentation:
For your second question, if you have storm control configured for multicast and a multicast storm occurs, it could potentially disrupt network protocols that rely on multicast traffic, like OSPF or EIGRP. These protocols could indeed lose neighbor relationships if the multicast traffic is blocked because they rely on multicast messages to establish and maintain neighbor relationships.
For this reason, storm control for multicast should be used carefully. You must weigh the potential benefits and drawbacks of the use of storm control in such situations.