3750, 4500 and Storm Control

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Jul 28th, 2010
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Hi all,

I'm going to activate Storm Control on Catalyst 3750 and 4506E but, as I understood from documentation,

the behavior changes depending on the fact that the feature is hardware-based or software-based. This is well explained on Cat4k configuration guide:

- sw-based means that if threshold for a certain type of traffic is reached, ALL the traffic on the interface is blocked

"..When the interface threshold is met, all incoming data traffic on the interface is dropped.."

- hw-based means that if threshold for a certain type of traffic is reached, that type of traffic is blocked

"... If the packetdestination address is broadcast, then the broadcast suppression circuitry tracks the current count of
broadcasts within the one-second interval, and when a threshold is reached, it filters out subsequent
broadcast packets.."

considering that I have /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Tabella normale"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;} Sup WS-X45-SUP6L-E, the data sheet ( http://www.cisco.com/en/US/partner/prod/collateral/switches/ps5718/ps4324/data_sheet_c78-530856.html ) reports that

Multicast and Broadcast Suppression are supported in hw for all ports

what about 3750? Does anyone know if it implements hw-based or sw-based Storm Control?

Another question on Storm Control is: is it technically correct that the switch shouldn't be able to distinguish L2 broadcast from multicast and that for this reason Multicast threshold should be configured higher than Broadcast one?

Thanks a lot

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zdesve33 Mon, 08/09/2010 - 05:05
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c3750 implements hw storm-control.

Your second question - i dont understand you, switch generally is able to distinguish broad- and multicasts, but sometimes storm-controls counts both types together. Practically i recommend implement shutdown action (with automatically recover), broacast-storm even sharpened by treshholds can slow down switch a troubleshooting is harder (and, of course, broadcasts still flood the lan).



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