RSTP and redundancy

[rgpetty]

Hello,
We need some advice regarding RSTP and redundancy. We’ve been having a difficult time with RSTP and multiple redundant paths coming into the same switch.

We have three remote locations using FSO lasers to communicate back to a central location. At each location there is also a Solectek radio for backup. All switches are configured for RSTP with the FSO ports having a lower cost and priority than the radio ports. Up until now we only had a single redundant leg installed and it worked ok. When the weather was bad and foggy the FSO would stop and the radio would take over after a few seconds and cut back to the FSO later when the weather improved. However, after installing a second redundant leg this past week (and a third one planned) the network locks up after about 5-6 minutes.

We were thinking our problem is with the multiple redundant paths coming into the same central switch. Can this be done or do we need more switches, one for each path? Hope someone may be able to help?

[Mohieddin Kharnoub]

Hi

Your issue is a technology issue not a product one.

You can have multiple links from one site to another, and this will cause a loop, and the Spanning-Tree job is to block these ports to insure a loop free topology.

Now our job is to play with the Priority and Path cost settings to ensure a practical and better topology.

I think you better have a double check on the configuration you have, and Syslog enabled on your switch for more debug details and events.

Good Luck !!!

[rgpetty]

Thanks for the response. Are you saying that, if I have three switches, a "central", a "remote1" and a "remote2", with both remotes having a redundant path back to the central switch, which would of course have two redundant paths terminating into it, it will work as long as I have my cost and priority configured correctly?

For example, the central switch port to the local network would have a cost of 200000? The 1st redundant path in the central switch would have a cost of 20000 for the primary port and 40000 for the secondary port? The second redundant path in the central switch would have a cost of 60000 for its primary port and 80000 for the secondary port?

[rgpetty]

Apparently this configuration is a lot more complicated than I thought. Weâ re in the process of setting up four switches here in the shop to see if we can duplicate the problem we had at the customerâ s location. Weâ ll then reconfigure with some modifications to the costs and priorities to see if that changes things. Hopefully this may give us a little more information as to whether or not you can have multiple redundant paths coming into the same switch.