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Broadcast storms and VLANs?

RicN
Valued Contributor

Broadcast storms and VLANs?


If I have my network segmented into VLANs and a broadcast storm for some reason enters one of the vlans, can I assume that my other vlans will be unaffected?

That is for example, on a typical switch is half the ports VLAN10 and the others are VLAN20, and a broadcast storm enters the lan from one of the VLAN10 ports. Will the VLAN20 users suffer from this?


3 REPLIES
Jack Howes
Frequent Advisor

Re: Broadcast storms and VLANs?

In theory the other vlan will not be affected. What I have seen is that any switch associcated with the VLAN experiencing the storm becomes so busy that it disrupts normal data flow on the other VLANs.
Matt Hobbs
Honored Contributor

Re: Broadcast storms and VLANs?

Unfortnately I have to agree with Jack, in theory it shouldn't but often it does.

There are a lot of features available now to prevent a broadcast storm really taking hold.

1. Spanning-tree
2. Loop-protect
3. Disabling auto-mdix on your edge ports
4. Broadcast/multicast rate-limiting (new feature on the 3500/5400).
RicN
Valued Contributor

Re: Broadcast storms and VLANs?


Thank you for your answers Jack and Matt!

Jack:

>In theory the other vlan will not be affected.
>What I have seen is that any switch associcated
>with the VLAN experiencing the storm becomes so
>busy that it disrupts normal data flow on the
>other VLANs.

Does it matter what capacity the switch have? If a switch should be able to deliver, say, 100 mbit/s at wirespeed on 24 ports, and 12 ports in VLAN 10 are trapped in a broadcast storm and are sending/recieving at 100mbit.
Should the capacity not be enought to have the other 12 ports in some other VLAN to send/recieve at normal speed?

Does it matter which switch model you are using?

Matt:

>2. Loop-protect

Do you know if loop-protect can detect loop on the same port? That is, if a end user is bringing for example a private hub to the office and attach it to a port on a corporate switch, and two hub ports by mistake are connected with a loop. Does the loop-protect feature on the Procurve detect this as loop, even if it the same port?

>3. Disabling auto-mdix on your edge ports

What would be the reason for this? I have not heard of that before, could auto-mdix increase the risk for loop/broadcast storms?

>4. Broadcast/multicast rate-limiting (new feature on the 3500/5400).

Do you know if that feature will be able available on some other switches than these?