Configuring the Rapid Spanning Tree Protocol
Original instructions
About us
Introduction
The Ethernet DEVICE NETWORK ports on the front of the BMENOC0301/11 Ethernet communications module (ETH 2, ETH 3) support the Rapid Spanning Tree Protocol. RSTP is an OSI layer 2 protocol defined by IEEE 802.1D 2004. The protocol performs these services:
NOTE: When an RSTP link is connected, the RSTP service acts on an event and forwards traffic through the correct port. During this re-connect time (50ms max), some packets may be lost.
RSTP software, operating simultaneously in all network switches, obtains information from each neighboring switch, which enables the software to create a hierarchical logical network topology. RSTP is a flexible protocol that can be implemented on many physical topologies, including ring, mesh, or a combination of ring and mesh.
NOTE: RSTP can be implemented only when all network switches are configured to support RSTP.
View the Page
Display the RSTP page:
Step
Action
1
Open a Control Expert project that includes a BMENOC0301/11 module.
2
Enable RSTP for the module on the Services page.
3
Open the DTM Browser (Tools → DTM Browser).
4
In the DTM Browser, find the name that you assigned to the BMENOC0301/11 module.
5
Double-click the name of the BMENOC0301/11 to open the configuration window.
NOTE: You can also right-click on the module and scroll to Open to open the configuration window.
6
Expand (+) Services in the navigation tree.
7
Select RSTP to see the two configuration tabs, General and Advanced.
NOTE: The Advanced tab appears only when you enable the DTM’s Advanced Mode
Assign the Bridge Priority
The bridge priority is a 2-byte value for the switch. The range for valid values is 0 ... 65535, with a default of 32768 (the midpoint).
Select the General tab to configure the Bridge Priority:
Step
Action
1
Select a Bridge Priority from the drop-down list in the RSTP Operational State area:
  • Root (0)
  • Backup Root (4096)
  • Participant (32768) (default)
2
Finish the configuration:
  • OK: Assign the Bridge Priority and close the window.
  • Apply: Assign the Bridge Priority and keep the window open.
NOTE: The Bridge Priority value is used to establish the relative position of the switch in the RSTP hierarchy.
Advanced Configuration
Select the Advanced tab to configure these parameters:
Field
Property
Description
Bridge Parameters
Maximum Age Time
The switch waits this length of time (6 ... 40 sec) for receipt of the next hello message before it initiates a change to the RSTP topology. (Default = 40 sec.)
Transmit Hold Count
The maximum number of BPDUs (1 ... 40) that the switch can transmit per second. (Default = 40.)
Hello Time
The embedded switch sends heartbeat BPDUs at this (read-only) frequency (2 sec).
Port Parameters
(ETH 2, ETH 3)
RSTP
This (read-only) property is set to Enabled in the Services page.
Priority
The priority assigned to the switch port, an integer from 0 to 240 in increments of 16. Default = 0. This value is used by the RSTP process if it needs to break a tie between two ports on the same switch when identifying a:
  • root port: the port on a non-root switch that is closest to the root bridge in terms of path cost, or
  • designated port: the port at one end of a network segment through which traffic passes on its way to the root bridge
RSTP Cost
Select a method to determine the RSTP cost of the path through the embedded switch:
  • Auto: The RSTP protocol automatically assigns a value to the switch by operation of the RSTP algorithm.
  • Manual: Input the RSTP cost integer (1 ... 200000000) in the Value field.
Edge Port
Set to a fixed (read-only) value of Auto. The RSTP process automatically determines if the port is an RSTP edge port.
Point to Point
(read-only) Set to a fixed value of Auto. The RSTP process automatically determines if the port is an RSTP point-to-point port.