Configuring the Rapid Spanning Tree Protocol
Original instructions
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Description
Ethernet ports 3 and 4, located on the front of the 140 NOC 78• 00 head module, support the Rapid Spanning Tree Protocol (RSTP). RSTP is an OSI layer 2 protocol defined by IEEE 802.1D 2004. RSTP performs 2 services:
RSTP software, operating simultaneously in all network switches, obtains information from each 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.
Use the RSTP → General and the RSTP → Advanced pages to configure RSTP for the embedded Ethernet switch in the 140 NOC 78• 00 head module.
NOTE: RSTP can be implemented only when all network switches are configured to support RSTP.
The RSTP → General page looks like this:
The RSTP → Advanced page looks like this:
NOTE: The Advanced page is available only when you enable advanced mode.
To display these pages:
Step
Description
1
Select the Services node in the navigation tree located on the left side of the Device Editor.
Result:The Services page opens.
2
In the Services page, set the RSTP field to Enabled, then click OK or Apply.
Result: The RSTP node appears in the navigation tree.
3
Select the RSTP node in the navigation tree, then click on either the General or Advanced tab to display that page.
NOTE: Refer to the topic Configuring Properties in the Device Editor for instructions on how to edit properties.
Configuring RSTP Properties
The following properties can be viewed and edited in the RSTP → General page:
Property
Description
RSTP Operational State: Bridge Priority
Select one of the following values in the drop-down list:
  • Root (0)
  • Backup Root (4096)
  • Participant (32768)
NOTE: Network switches running RSTP software periodically exchange information about themselves using special packets called Bridge Protocol Data Units (BPDUs), which act as a heartbeat. The Bridge Priority value is contained in the BPDU and establishes the relative position of the switch in the RSTP hierarchy.
The following properties can be viewed and edited in the RSTP → Advanced page:
Property
Description
Bridge Parameters:
Maximum Age Time
This value is set to The length of time, from 6 to 40 seconds, that the switch waits for receipt of the next hello message, before initiating a change to the RSTP topology. Default = 40 s.
Transmit Hold Count
The maximum number of BPDUs, from 1 to 40, that the switch can transmit per second. Default = 40.
Hello Time
(read-only) The frequency—set at 2 seconds—that the embedded switch sends heartbeat BPDUs.
Port Parameters (These properties can be separately configured for ports 3 and 4):
RSTP
(read-only) This 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
Path Cost
The method used to determine the path cost through the embedded switch. Values include:
  • Auto: The RSTP protocol automatically assigns a value to the switch by operation of the RSTP algorithm.
  • Manual: Input the RSTP cost — an integer from 1 to 200000000 — in the Value field.
Edge Port
(read-only) Set to a fixed 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.