Reduce Broadcast frames.

Unanswered Question
May 9th, 2008


I am Network Engineeer. In my network totally 3 vlans with 250 users. Now I analyse the network through FLUKE Lan Analyser. I got 100 % Broadcast in my network. I want to reduce the Broadcast. I use Cat 4503 chassis as a L3 switch.

Please guide me.

I have this problem too.
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alessandro.veras Fri, 05/09/2008 - 00:51

Hi psaravanan !

I belive the most important thing is to evaluate which applications are generating this broadcasts.

But you can use the following commands at the switch ports to control this broadcasts:

storm-control broadcast level < percentage > storm-control multicast level < percentage >

I hope this helps.


Alessandro Veras

psaravanan Tue, 05/20/2008 - 23:48

hello sir,

My network Broadcast to 95%.

Suppose I configure Broadcast strom configuration, then what will happen in that network, whether network utilization will increase or Network Bandwidth will increase.

Please tell me sir or please suggest any link about the topic.

andrew.butterworth Wed, 05/21/2008 - 00:10

Is it possible you are just monitoring on a switch port and you are ONLY seeing broadcast frames and the switch is doing it's job correctly? If you have just plugged a fluke into an switched access port then the switch will discover the fluke's MAC address (if it transmits anything) and only forward traffic specifically to it's MAC address as well as broadcasts & multicasts within the VLAN.

It might be worth explaining what you have configured to enable this 'monitoring'.


ebanks2006 Wed, 05/21/2008 - 02:55

I tend to agree with Andrew. If your network was truly experiencing 100% broadcast traffic in the sense that you mean it - i.e. all your segments full to capacity with broadcast frames - then your network would be non-functional.

Is your network working? Are users able to run their applications, performance is adequate, etc? Then you probably don't have a problem with broadcast traffic. As Andrew pointed out, the Fluke might be seeing a lot of broadcast frames on the interface you happen to be plugged into.

Did you configure the interface you plugged the Fluke into to be a span or monitor port? If you didn't, all you're going to see are broadcast frames. The Fluke will never see unicast traffic destined for other interfaces without a span set up. The Fluke will only see traffic that happens to come across the interface you plugged the Fluke into - broadcast traffic.

If you want to see ALL the traffic flowing through your 4503 (unicast AND broadcast), you need to configure the 4503 to send copies of all frames it sees to the interface you plugged the Fluke into. This is done using a span session. Perhaps you're already running a span session. But if not, take a look at this link that will explain to you how to set it up.

psaravanan Wed, 05/21/2008 - 03:42

Actually I want to see entire vlan broadcast not for the 4503 switch broadcast.

How do increase Network Utilization?

Please give me the link of Network Maintanence or Broadcast reducing and Increase Network Bandwidth

ebanks2006 Wed, 05/21/2008 - 04:07

You need to use SPAN to see the entire VLAN traffic, both unicast and broadcast. The link I posted in the previous message explains how to set this up.

I doubt you have a problem with broadcast traffic from what you have written. But let's assume, for sake of argument, you really have a crippling broadcast storm that's consuming 100% of your network bandwidth. The simplest way to deal with broadcast storms is to use storm-control. Using storm-control will accomplish, in your words, "broadcast reducing" and "increase network bandwidth".

psaravanan Fri, 05/30/2008 - 05:04

Thanks for your reply,

Each port Broadcast is very low like 0.1 to 3%, but total network ie. network address broadcast is 100%.

for example, network. Each user broadcast is very low, but the got 95% broadcast. How do reduce these broadcast.

I have four vlans with cat4503 and 1700 router.

Each port broadcast is not required. please help me.


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