3560/3550 Storm control behavior

[mkamar]

-I've read in 3550 cisco documentation that " When the rate of multicast traffic exceeds a set threshold, all incoming traffic (broadcast, multicast, and unicast) is dropped until the level drops below the threshold level. Only spanning-tree packets are forwarded. When broadcast and unicast thresholds are exceeded, traffic is blocked for only the type of traffic that exceeded the threshold" The question is this applied also for 3560 ???

-The 2nd question is how i can rate-limit BW using this feature, because as you know, u have to determine the level of each type of traffic seperatly (Broadcast, multicast and unicast), I mean nothing let me determine the level of all traffic, thanks

[ariela]

Hi,

first answer

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the behavior is a little different:

on 3550

"When the rate of multicast traffic exceeds a set threshold, all incoming traffic (broadcast, multicast, and unicast) is dropped until the level drops below the threshold level. Only spanning-tree packets are forwarded. When broadcast and unicast thresholds are exceeded, traffic is blocked for only the type of traffic that exceeded the threshold."

on 3560

"When the storm control threshold for multicast traffic is reached, all multicast traffic except control traffic, such as bridge protocol data unit (BDPU) and Cisco Discovery Protocol (CDP) frames, are blocked. However, the switch does not differentiate between routing updates, such as OSPF, and regular multicast data traffic, so both types of traffic are blocked."

for more details about differences between 3550 and 3560 please take a look at:

http://www.cisco.com/en/US/docs/switches/lan/catalyst3550/software/release/12.2_25_see/configuration/guide/swtrafc.html#wp1063295

http://www.cisco.com/en/US/docs/switches/lan/catalyst3560/software/release/12.2_25_see/configuration/guide/swtrafc.html#wp1063295

second answer

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The question is too generic, and my answer is "it depends". The best thing is to monitor your network, check multicast and unicast requirements, keep in mind some generic rules (example: you should set Multicast limit HIGHER than the Broadcast limit), check your hardware platform (3550? 3560? whatever?) and the related documentation, and check how your storm control rules will be applied (with show storm-control command). Please let me know if I could be more helpful.

A good start point:

http://cauew.blogspot.com/2008/09/storm-control-everything-you-need-to.html

HTH

Andrea

[mkamar]

Hi Andrea;

Thanks for your answeres,

1st answer

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Still Cisco documentation is not very clear in the 1st question, Does it mean that in the 3560 when multicasting threeshold reached only multicast traffic is blocked, and unicast and broadcast are not affected which is not the case in 3550 ???

2nd answer

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that means using storm control to limit the BW require to specify the limit of each type specefically, like 40%unicast,40%multicast and 20% unicast? in other words nothing can be done using this command to limit the total BW to let's say 20% from the port BW

Finally, thank you very much for your great help

[ariela · Accepted solution]

Hi,

about 1st answer,

the Cisco documentation is not very clear, I see ... In my understanding, when multicasting threeshold reached, all traffics are blocked (that is multicast, unicast and broadcast), like 3550. But the difference seems to be that: on 3560 all control traffics are not blocked (STP, CDP, ...), on 3550 only STP. Does make sense?

The best thing, as normally happens, is test in a lab the documentation ;)

about 2nd answer,

none ... you could specify only the type of traffic that you would control.

Another good link to understand that feature:

http://tcpmag.com/qanda/article.asp?EditorialsID=287

Let me know if it's clear enough.

HTH

Andrea

[mkamar]

Hi Andrea;

This is exactly what i want reach, your answeres were extermly helpful, So many thanks man