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CAT 3560 / Broadcast Storms


Is there any way to control Broadcasts/ storms on our LAN. We have a very flat network. 3 x CAT 3350's going into a Cat 3560 with around 40 hosts per switch.

We'd like to block/dampen broadcasts coming from the hosts on the three 3350's, I saw the "set port broadcast" command but this does not seem to be a feature with these switches, any ideas?


J mac


Re: CAT 3560 / Broadcast Storms

When using multiple vlans in a network, a good rule of thumb is to limit a vlan size to no more than 254 hosts per vlan. Since you have less then that, you should not be seeing severe issues with broadcast. I would look at some of the traffic to make sure is all legit. Also, it would be good for you to start segmenting your network with layer3 boundaries. Since you are have 3550s and 3560s to work with, this is what I would do:

Use the 3560 as my core switch

Each user segment on a different switch should be in a different vlan

On the 3560, create an SVI for each vlan

Tag the appropriate ports for each vlan and allow for proper inter-vlan routing.

Hope this helps.

New Member

Re: CAT 3560 / Broadcast Storms

Thats very helpful thanks. Am i able to do this without the need of a router?

Could i do this use the Fibre Gig ports for the trunks?

Does anyone have any good documentation on configuring this.

Many Thanks


Re: CAT 3560 / Broadcast Storms


when you say 3350 switches, I assume you mean the 3550's ? Both the 3550 and the 3560 switches have the interface command 'storm-control broadcast level' available. When you e.g. set the level to 20 (percent), broadcast traffic exceeding that threshold will be dropped until it falls back under that level. Check this link for details:

Configuring Storm Control



Re: CAT 3560 / Broadcast Storms


in addition to Sean's post, just be aware that segmenting your network (actually introducing Layer 3 SVI's) might negatively affect the performance of your network, since all traffic between the segments now has to be routed instead of switched. I would also try and find out first what causes the excessive broadcasts (it could simply be a broken NIC in one of the PC's), since even with segmenting your network, the clients in the same network segment would probably still have the same problem.



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