STP - UplinkFast and root port delay timer


[UplinkFast](/stp-uplinkfast) is a Cisco proprietary enhancement to the original [Spanning Tree Protocol (STP)](/spanning-tree-protocol-stp) designed to improve convergence times. When a root port fails, UplinkFast allows a switch to quickly transition an alternate port to the forwarding state, reducing downtime. However, the [root port delay timer](/stp-uplinkfast-and-root-port-delay-timer) of 50 seconds (non-configurable) is employed when the original root port comes back up.

There are situations in which STP reconvergence will occur faster than the delay timer of 50 seconds.  This can depend on various factors:

1. **Platform Variability**: UplinkFast is not part of the original 802.1D STP design, so it is not strictly adhered to, and its implementation may vary across different Cisco platforms.
2. **STP Version Impact**: The behavior of UplinkFast can be affected by the STP version in use. For instance, [Rapid Spanning Tree Protocol (RSTP)](/stp-rstp-convergence-process) inherently reconverges quickly, rendering UplinkFast configurations less impactful.

Understanding these factors can help in optimizing network performance and ensuring quick recovery from link failures using UplinkFast.

Links:

https://forum.networklessons.com/t/spanning-tree-uplinkfast/1140/73?u=lagapidis

https://networklessons.com/spanning-tree/spanning-tree-uplinkfast

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STP - UplinkFast and reconvergence

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