Technical data

BLADE OS 5.1 Application Guide
84
 Chapter 5: Spanning Tree Group BMD00136, November 2009
Port Fast Forwarding
Port Fast Forwarding permits a port that participates in Spanning Tree to bypass the Listening and
Learning states and enter directly into the Forwarding state. While in the Forwarding state, the port
listens to the BPDUs to learn if there is a loop and, if dictated by normal STG behavior (following
priorities, etc.), the port transitions into the Blocking state. This feature permits the G8000 to
interoperate well within Rapid Spanning Tree (RSTP) networks.
Use the following CLI commands to enable Port Fast Forwarding on a port (Interface Port mode):
Remember to apply and save your configuration changes.
Fast Uplink Convergence
Fast Uplink Convergence enables the G8000 to quickly recover 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 multicasts addresses in the forwarding database (FDB)
and ARP table over the secondary link so that upstream switches can learn the new path.
Configuration Guidelines
When you enable Fast Uplink Convergence, BLADE OS automatically makes the following
configuration changes:
 Sets the bridge priority to 65535 so that it does not become the root switch.
 Increases the cost of all of the interface ports by 3000, 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 command to enable Fast Uplink Convergence on ports.
>> # spanning-tree stp <STG number> fastforward
>> # spanning-tree uplinkfast