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Spanning Tree Protocol
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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 switch to interoperate well with Fast Path, a NIC Teaming feature.
Configuring Port Fast Forwarding
Use the following CLI commands to enable Port Fast Forwarding on an external port.
>> # /cfg/l2/stp 1/port 20 (Select port 20)
>> Spanning Tree Port 20# fastfwd ena (Enable Port Fast Forwarding)
>> Spanning Tree Port 20# apply (Make your changes active)
>> Spanning Tree Port 20# save (Save for restore after reboot)
Fast Uplink Convergence
Fast Uplink Convergence enables the switch 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 60
seconds, while the backup link transitions from Blocking to Listening to Learning and then Forwarding
states. With Fast Uplink Convergence enabled, the switch 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.
Configuration guidelines
When you enable Fast Uplink Convergence, the switch software automatically makes the following
configuration changes:
• Increases the bridge priority to 65500 so that it does not become the root switch.
• Increases the cost of all of the external ports by 3000, across all VLANs and Spanning Tree Groups.
This ensures that traffic never flows through the switch to get to another switch unless there is no
other path.
When you disable Fast Uplink Convergence, the bridge priorities and path cost are set to their default
values for all STP groups.
Configuring Fast Uplink Convergence
Use the following CLI commands to enable Fast Uplink Convergence on external ports:
>> # /cfg/l2/upfast ena(Enable Fast Uplink convergence)
>> Layer 2# apply(Make your changes active)
>> Layer 2# save(Save for restore after reboot)