User guide

Chapter 5
Setup and Configuration
RUGGEDCOM ROS
User Guide
142 RSTP Port Redundancy
The strategy that should be used is to assign each bridge’s priority to correspond to its distance from the root
bridge. If the root bridge is assigned the lowest priority of 0, the bridges on either side should use a priority
of 4096 and the next bridges 8192 and so on. As there are 16 levels of bridge priority available, this method
provides for up to 31 bridges in the ring.
6. Decide upon a port cost calculation strategy.
It is recommended to use the auto-negotiated cost style, unless it is necessary for the network design to
change the auto-negotiated cost style. Select whether the STP or RSTP cost style should be used. Make
sure to configure the same cost style on all devices on the network.
7. Disable RSTP Fast Root Failover option.
This is a proprietary feature of Siemens . In ROS, the RSTP Fast Root Failover option is enabled by default.
It is recommended to disable this feature when operating in a Ring network.
8. Implement the network and test under load.
Section 5.3.2.3
RSTP Port Redundancy
In cases where port redundancy is essential, RSTP allows more than one bridge port to service a LAN. In the
following example, if port 3 is designated to carry the network traffic of LAN A, port 4 will block traffic. Should an
interface failure occur on port 3, port 4 will assume control of the LAN.
A
1 2
3
4
Figure 93: Example - Port Redundancy
Section 5.3.3
Configuring STP Globally
To configure global settings for the Spanning Tree Protocol (STP), do the following:
1. Navigate to Spanning Tree » Configure Bridge RSTP Parameters. The Bridge RSTP Parameters form
appears.