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BLADEOS 6.5.2 Application Guide
BMD00220, October 2010 Chapter 8: Spanning Tree Protocols 113
Port Priority
The port priority helps determine which bridge port becomes the root port or the designated port.
The case for the root port is when two switches are connected using a minimum of two links with
the same path-cost. The case for the designated port is in a network topology that has multiple
bridge ports with the same path-cost connected to a single segment, the port with the lowest port
priority becomes the designated port for the segment. Use the following command to configure the
port priority:
Note – where priority value is a number from 0 to 255.For RSTP, MSTP, and PVRST modes, port
priority must be specified in increments of 16.
Port Path Cost
The port path cost assigns lower values to high-bandwidth ports, such as 10 Gigabit Ethernet, to
encourage their use. The objective is to use the fastest links so that the route with the lowest cost is
chosen. A value of 0 (the default) indicates that the default cost will be computed for an
auto-negotiated link or trunk speed.
Use the following command to modify the port path cost:
The port path cost varies, depending on Spanning Tree mode, as follows:
STP/PVST+: 1-65535
RSTP/PVRST/MSTP: 1-200000000 (0 = automatic path cost)
Fast Uplink Convergence
Fast Uplink Convergence enables the G8124 to quickly recover from the failure of the primary link
or trunk group in a Layer 2 network using STP/PVST+ mode. Normal recovery can take as long as
50 seconds, while the backup link transitions from Blocking to Listening to Learning and then
Forwarding states. With Fast Uplink Convergence enabled, the G8124 immediately places the
secondary path into Forwarding state, and multicasts the addresses in the forwarding database
(FDB) and ARP table over the secondary link so that upstream switches can learn the new path.
Note – In order for Fast Uplink Convergence to be functional, the switch must be running in
STP/PVST mode and must be linked to switches running STP, PVST, or PVST+.
RS G8124(config)# spanning-tree stp <STG> priority <priority value>
RS G8124(config)# interface port <port number>
RS G8124(config-if)# spanning-tree stp <STG> path-cost <path cost value>
RS G8124(config-if)# exit