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46 Dell Converged Enhanced Ethernet Administrator’s Guide
53-1002116-01
RSTP overview
6
With RSTP, the port roles for the new interface states are also different. RSTP differentiates
explicitly between the state of the port and the role it plays in the topology. RSTP uses the root port
and designated port roles defined by STP, but splits the blocked port role into backup port and
alternate port roles:
• Backup port—Provides a backup for the designated port and can only exist where two or more
ports of the switch are connected to the same LAN; the LAN where the bridge serves as a
designated switch.
• Alternate port—Serves as an alternate port for the root port providing a redundant path towards
the root bridge.
Only the root port and the designated ports are part of the active topology; the alternate and
backup ports do not participate in it.
When the network is stable, the root and the designated ports are in the forwarding state, while the
the alternate and backup ports are in the discarding state. When there is a topology change, the
new RSTP port roles allow a faster transition of an alternate port into the forwarding state.
For more information on RSTP, see “STP, RSTP, and MSTP configuration and management” on
page 51.
Configuring RSTP on Dell FCoE hardware
The basic process for configuring RSTP on your Dell FCoE hardware is as follows.
1. Enter Global Configuration mode.
2. Enable RSTP using the global protocol spanning-tree command. For details, see “Enabling STP,
RSTP, or MSTP” on page 51.
switch(config)#protocol spanning-tree rstp
3. Designate the root switch using the bridge-priority command. For details, see “Specifying the
bridge priority” on page 52. The range is 0 through 61440 and the priority values can be set
only in increments of 4096.
switch(conf-stp)#bridge-priority 28582
4. Configure the bridge forward delay value. For details, see “Specifying the bridge forward delay”
on page 52.
switch(conf-stp)#forward-delay 20
5. Configure the bridge maximum aging time value. For details, see “Specifying the bridge
maximum aging time” on page 53.
switch(conf-stp)#max-age 25
6. Enable the error disable timeout timer value. For details, see “Enabling the error disable
timeout timer” on page 53.
switch(conf-stp)#error-disable-timeout enable
7. Configure the error-disable-timeout interval value. For details, see “Specifying the error disable
timeout interval” on page 53.
8. switch(conf-stp)#error-disable-timeout interval 60
9. Configure the port-channel path cost. For details, see “Specifying the port-channel path cost”
on page 54.
switch(conf-stp)#port-channel path-cost custom