Broadcast storms and VLANs?

[RicN]

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?

[Jack Howes]

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]

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]

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?