RackSwitch G8000 Application Guide
Chapter 5: Spanning Tree
91BMD00041, November 2008
Fast Uplink Convergence
Fast Uplink Convergence enables the G8000 to recover quickly from the failure of the primary
link or trunk group in a Layer 2 network using Spanning Tree Protocol. 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 G8000
immediately places the secondary path into Forwarding state, and sends multicasts of
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
PVRST+ mode and must be linked to switches running STP/PVST.
Configuration Guidelines
When you enable Fast Uplink Convergence, the G8000 automatically makes the following
configuration changes:
Sets the bridge priority to 61440 so that it does not become the root switch.
Increases the cost of all ports by 30000, across all VLANs and Spanning Tree Groups.
This ensures that traffic never flows through the G8000 to get to another switch unless
there is no other path.
These changes are reversed if the feature is disabled.
Configuring Fast Uplink Convergence
Use the following CLI commands to enable Fast Uplink Convergence on all ports.
RS G8000 (config)# spanning-tree uplinkfast
