RuggedCom RS400 manual Problem Five, Problem Six, Problem Seven

Spanning Tree

Problem Three

When I test your switch by deliberately breaking a link, it takes a long time before I can poll devices past the switch. I thought RSTP was supposed to be fast. What is happening?

Is it possible that ports participating in the topology have been configured to STP mode or that the port’s point-to-point parameter is set false? STP and multipoint ports converge slowly after failures occur.

Is it possible that the port has migrated to STP? If the port is connected to the LAN segment by shared media and STP bridges are connected to that media then convergence after link failure will be slow.

Delays on the order of tens or hundreds of milliseconds can result in circumstances where the link broken is the sole link to the root bridge and the secondary root bridge is poorly chosen. The worst of all possible designs occurs when the secondary root bridge is located at the farthest edge of the network from the root. In this case a configuration message will have to propagate out to the edge and then back in order to reestablish the topology.

Problem Four

My network is composed of ring of bridges of which two (connected to each other) are managed and the rest are unmanaged. Why does the RSTP protocol work quickly when I break a link between the managed bridges but not in the unmanaged bridge part of the ring?

A properly operating unmanaged bridge is transparent to configuration messages. The managed bridges will exchange configuration messages through the unmanaged bridge part of the ring as if it is non-existent. When a link in the unmanaged part of the ring fails however, the managed bridges will only be able to detect the failure through timing out of hello messages. Full connectivity will require three hello times plus two forwarding times to be restored.

Problem Five

The switch is up and running and working fine. Then I start a certain application and the network becomes unstable. After I stop the application the network goes back to running normally.

RSTP sends its configuration messages using the highest possible priority level. If CoS is configured to allow traffic flows at the highest priority level and these traffic flows burst continuously to 100% of the line bandwidth, STP may be disrupted. It is therefore advised not to use the highest CoS.

Problem Six

After I bring up a new port the root moves on to that port, and I don’t want it to. The port that I want to become root won’t do so.

Is it possible that the port cost is incorrectly programmed or that auto-negotiation derives an undesired value? Inspect the port and path costs with each port active as root.

Problem Seven

My IED/Controller doesn’t work with your switch.

Certain low CPU bandwidth controllers have been found to behave less than perfectly when they receive unexpected traffic. Try disabling STP for the port.

RS400 167 ROS™ v3.5