Sep
07
Fast Convergence for Designated Ports RSTP protocol's fast convergence depends on the use of point-to-point links connecting switches. In order to quickly transition a designated port into non-discarding state, the upstream switch needs to make sure that the downstream neighbor agrees with that idea. This constitutes the process known as handshake (or proposal/agreement): Upstream bridge sends a proposal out of a designated port. As a matter of fact, it just sets the proposal bit in outgoing... Read More
Mar
14
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: http://blog.ine.com/wp-content/uploads/2010/04/understanding-stp-rstp-convergence.pdf UplinkFast Read More
Mar
07
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

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