Configuring the Rapid Spanning Tree Protocol
Original instructions
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Introduction
The Ethernet control network ports (ETH 2, ETH 3) on the front of the BMENOC0321 control network module 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, some packets may be lost.
  • The reconnection time is 50ms maximum when all devices in the RSTP domain have the same behavior.
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 BMENOC0321 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 BMENOC0321 module.
5
Double-click the name of the BMENOC0321 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 when Advanced Mode is enabled:
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. 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.