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How managed switches handle Broadcast Multicast and Unicast?

An application published broadcast message to a network, and caused network switch to drop packet. I have been told this is a Broadcast Storm.

I'd like to understand

On a typical managed switch (1Gb Ethernet/10Gb Ethernet),

a) how many broadcast message can it handle, without causing a broadcast storm?

b) what is the bandwidth and latency characteristics when a switch is handling broadcast messages, under low/median/high load?

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marked as duplicate by EEAA, MDMarra, pauska, Hyppy, Chris S Jun 1 '11 at 15:25

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What is your definition of a "typical" managed switch? Is this a $200 netgear or a $20k Cisco Cat6.5k? –  EEAA Jun 1 '11 at 15:12
    
By the way, why is there concern? What happened that was bad? The way Ethernet works, packets are dropped all the time. –  KCotreau Jun 1 '11 at 15:21
    
To ErikA: $20k cisco Cat6.5k –  Anthony S. Jun 1 '11 at 15:22
    
because i want to know how many broadcast messages can a switch handle specifically. I am sending hundreds of broadcast message per second, causing high CPU load on switch, and caused some unintended side effects to other applications (ping message dropped by switch, other application thought network is down, and triggered failover) –  Anthony S. Jun 1 '11 at 15:27
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1 Answer

That is not what I would call a broadcast storm. Usually a broadcast storm is caused by a bad piece of hardware, often a NIC. The NIC tries to communicate with another NIC, but it does what it referred to as jabbering, or spewing nonsense (in an Ethernet sense). This causes retries, which cause more retries, and flood the network. Virtually everything can be brought to a halt.

http://en.wikipedia.org/wiki/Broadcast_Storm

There is no standard number of broadcasts a switch can handle...it would depend on the switch, but most can still be overcome by a broadcast storm if they are not managed and have the ability to safeguard against them. I am not really sure what you want to know with the last part of your question.

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thx KCotreau, I simply think a few hundred broadcast message per second should not cause any issue... Do you think a Cisco Cat6.5k can handle thousands, 10ks, or > broadcast messages per second? –  Anthony S. Jun 1 '11 at 15:29
    
A broadcast storm is caused by software, or misconfigured hardware (like two switches w/o STP). A bad NIC that's cattering (never heard "Jabbering" used before, probably a regional thing) will down the link and any hubs connected to it, but a switch will not forward that bad traffic to the whole network. –  Chris S Jun 1 '11 at 15:30
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