We are going to discuss Cisco’s proprietary extensions to STP algorithm, namely UplinkFast and BackBone Fast. Those two features aim to reduce the time it takes STP to re-activate topology after a link failure. While UplinkFast seems pretty intuitive, BB Fast is more complicated. See more detailed overview at: UplinkFast Read More
In this post we are going to look into STP convergence process. Many people have perfect understanding of STP, but yet face difficulties when they see questions like “How many seconds will it take for STP to recover connectivity if a given link fails?”. The post will follow the outline below: 1) General overview of STP convergence process 2) How STP converges if a directly connected link fails 3) How STP converges when it detects indirect link failure 4) Topology changes and their effect See... Read More
Cisco switches run different types of STP protocol, depending on whether the connected port is access, ISL trunk or 802.1q trunk. Natively, Cisco switch runs a separate STP instance for each configured and active VLAN (this is called Per-VLAN Spanning Tree or PVST) and standard IEEE compliant switches run just one instance of STP shared by all VLANs. Due to that reason, a group of switches running IEEE compatible STP protocol is called MST (Mono Spanning Tree) region, not to be confused with... Read More

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