network storm an issue?

[xp]

Hi,
if we have a network with 8 switches (3550 and nortel 450) (at 4 locations) in a ring, how long will the network take to recover from a break in the ring? I have been told a broadcast storm following the break could cause a traffic loss for up to 60 seconds. Is this likely? Any other suggestions for the network configuration?

Thanks,
Brian

 

[rcs2749]

Well if I read this right you are not operating in a ring. STP will disable one of the links to prevent broadcast storms. What happens if you develop a break somewhere else? The link that is disabled should come back online.

 

[baddos]

rcs2749 is correct if your running spanning tree. If you aren't, your network won't work in a ring.

Basically right now one of the links is in Blocking mode. When a break happens in your "ring", STP will start multicasting (not broadcasting) the topology change notification (TCN). When your other switches receive this special frame, it will reconfigure it's spanning tree and compute which interfaces should be put into forwarding mode or blocking mode. By default, your switches should bring up the redundant link in 15 seconds, after receving the TCN frame.

This isn't a broadcast storm. A broadcast storm is caused by a loop in your network that isn't protected by spanning-tree. With a default spanning-tree configuration, this should never happen.

 

[xp]

Thanks for the info. I will have the switches in a ring, with stp enabled. I was concerned about the recovery time if we had a fibre break at a point in the ring. I should have said multicasting for a new path, but the loss of traffic is the major concern. So 15 secs is the answer I was really looking for, thanks fellas.