Foundry Configuration Guide for the FESX, FSX, and FWSX
7 - 44 © Foundry Networks, Inc. December 2005
For example, in Figure 7.23, Switch 10 and Switch 30 receive legacy BPDUs from Switch 20. Ports on Switch 10
and Switch 30 begin sending BPDUs in STP format to allow them to operate transparently with Switch 20.
Figure 7.23 802.1W Bridges with an 802.1D Bridge
Once Switch 20 is removed from the LAN, Switch 10 and Switch 30 receive and transmit BPDUs in the STP format
to and from each other. This state will continue until the administrator enables the force-migration-check
command to force the bridge to send RSTP BPDU during a migrate time period. If ports on the bridges continue to
hear only STP BPDUs after this migrate time period, those ports will return to sending STP BPDUs. However,
when the ports receive RST BPDUs during the migrate time period, the ports begin sending RST BPDUs. The
migrate time period is non-configurable. It has a value of three seconds.
NOTE: The IEEE standards state that 802.1W bridges need to interoperate with 802.1D bridges. IEEE
standards set the path cost of 802.1W bridges to be between 1 and 200,000,000; whereas path cost of 802.1D
bridges are set between 1 and 65,535. In order for the two bridge types to be able to interoperate in the same
topology, the administrator needs to configure the bridge path cost appropriately. Path costs for either 802.1W
bridges or 802.1D bridges need to be changed; in most cases, path costs for 802.1W bridges need to be changed.
Configuring 802.1W Parameters on a Foundry Device
The remaining 802.1W sections explain how to configure the 802.1W protocol in a Foundry device.
Foundry devices are shipped from the factory with 802.1W disabled. Use the following methods to enable or
disable 802.1W. You can enable or disable 802.1W at the following levels:
• Port-based VLAN – Affects all ports within the specified port-based VLAN. When you enable or disable
802.1W within a port-based VLAN, the setting overrides the global setting. Thus, you can enable 802.1W for
the ports within a port-based VLAN even when 802.1W is globally disabled, or disable the ports within a port-
based VLAN when 802.1W is globally enabled.
• Individual port – Affects only the individual port. However, if you change the 802.1W state of the primary port
in a trunk group, the change affects all ports in the trunk group.
Enabling or Disabling 802.1W in a Port-Based VLAN
Use the following procedure to disable or enable 802.1W on a device on which you have configured a port-based
VLAN. Changing the 802.1W state in a VLAN affects only that VLAN.
To enable 802.1W for all ports in a port-based VLAN, enter commands such as the following:
FESX424 Router(config)# vlan 10
FESX424 Router(config-vlan-10)# spanning-tree 802-1w
Syntax: [no] spanning-tree 802-1w
Enabling or Disabling 802.1W on a Single Spanning Tree
To enable 802.1W for all ports of a single spanning tree, enter a command such as the following:
FESX424 Router(config-vlan-10)# spanning-tree single 802-1w
Syntax: [no] spanning-tree single 802-1w
Switch 10
20Switch
30Switch
802.1W
802.1W
802.1D
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