Quick Reference Guide

PowerConnect B-Series TI24X Configuration Guide 135
53-1002269-02
Configuring STP related features
6
For example, in Figure 24, 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 24 802.1W 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 device
The remaining 802.1W sections explain how to configure the 802.1W protocol in a device.
NOTE
With RSTP running, enabling static trunk on ports that are members of VLAN 4000 will keep the
system busy for 20 to 25 seconds.
PowerConnect 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.
Switch 10
Switch 20
Switch 30
802.1W
802.1D
802.1W