Rstp Port Redundancy; Mstp Operation - Siemens RUGGEDCOM ROX II User Manual

Chapter 5
Setup and Configuration
Decide upon a port cost calculation strategy.
6.
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 RUGGEDCOM ROX II, 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 5.36.2.3

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.
Figure 16: Example - Port Redundancy
Section 5.36.3

MSTP Operation

The Multiple Spanning Tree (MST) algorithm and protocol provide greater control and flexibility than RSTP and
legacy STP. MSTP (Multiple Spanning Tree Protocol) is an extension of RSTP, whereby multiple spanning trees
may be maintained on the same bridged network. Data traffic is allocated to one or several spanning trees by
mapping one or more VLANs to different Multiple Spanning Tree Instances (MSTIs).
The sophistication and utility of the MSTP implementation on a given bridged network is proportional to the
amount of planning and design invested in configuring MSTP.
If MSTP is activated on some or all of the bridges in a network with no additional configuration, the result will
be a fully and simply connected network. At best though, the result will be the same as a network using only
RSTP. Taking full advantage of the features offered by MSTP requires a potentially large number of configuration
variables to be derived from an analysis of data traffic on the bridged network, and from requirements for load
sharing, redundancy, and path optimization. Once these parameters have all been derived, it is also critical they
are consistently applied and managed across all bridges in an MST region.
By design, MSTP processing time is proportional to the number of active STP instances. This means MSTP will
likely be significantly slower than RSTP. Therefore, for mission critical applications, RSTP should be considered a
better network redundancy solution than MSTP.
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RUGGEDCOM ROX II
CLI User Guide
RSTP Port Redundancy