Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. And see here for current known issues.

New Member

Broadcast on switch fabric

Please I have switches on my network, all connected to a multilater switch with trunking and mant VLAN.I normaly have series of broadcast on the LAN. Please how can I detect broadcast,the source,the vlan and the particular switch.

2. If a cable is remove from any port on any switch on any VLAN,will I know by checking ''terminal monitor ''on any switch.

New Member

Re: Broadcast on switch fabric

Please reply this post

New Member

Re: Broadcast on switch fabric

Hi Just,

I am not sure,if I understood your questions,but I will try to answer according to what I believed it what you want.

1. "Please how can I detect broadcast,the source,the vlan and the particular switch.".

Each Vlan has separate Broadcast and by doing show "Vlan brief" you can know which vlan belong to which Broadcast.

"Show int trunk or Show vtp" ,will show you which source and the port. Also you can try "show interface Status". It will shows you which port is connected. finally, try "Show cdp neighbour or show cdp neighbour detail". This will show each source to your connection sand the appliances(switches)with their Vlans.



Hall of Fame Super Gold

Re: Broadcast on switch fabric

I had an issue like this a few years back. My client has one BIG FAT Layer 2 network (1 VLAN only!). We have a broadcast storm happening every afternoon around 5 pm. It took time, but we found out that it was caused by a Cisco switch being turned OFF when the owner would go home. It was also caused by the fact that portfast was enabled at both ports.

Unfortunately, it was no quick fix. We all had to trawl through the switch (3500XL running XU IOS) and find out which ports should have portfast turned off.

My suspicion is that you are in the same situation as I do. Enable spanning-tree bpduguard (globally or interface) and this should shut down ports where possible loops are coming from and fix each ports as you go.

New Member

Re: Broadcast on switch fabric

yeah, thnx for reply. What I am saying is that. there was a time we had loop or broadcast issue where the return time is around 200 instead of 1. Its a network with many switches connected with many VLAN. what I need is a way to detect the loop on the network, either through 'terminal emulator' or any effective tools

New Member

Re: Broadcast on switch fabric


What i will suggest is to do some fine tuining of your network .

Of course you will have broadcast storm if you have a FAT L2 network with only 1 vlan.

Because if the switch will not know the destination it will send broadcast.

Probably you could configure broadcast storm on the links which will help , you could do it in such a way that if the

broadcast traffic increase it will shut the port and send the trap so you will know about the issue and where it is.



New Member

Re: Broadcast on switch fabric

Well, thanks I have many vlans configure,what I need to know is how to go about it when when broadcast happen. Can I know through terminal emulator where the loop/broadcast from.

New Member

Re: Broadcast on switch fabric

Anyone there?

CreatePlease to create content