When I studied for my CCIE almost 15 years ago, I recall that I was fascinated by how different PDUs such as CDP, DTP, STP would have different encapsulations on a trunk depending on the configuration of it. What happens
Detecting Mismatched Native VLANs
Many people have seen the message logged to their switch about a mismatched native VLAN on a trunk, but how is it detected? There are two methods of detecting mismatched native VLAN on a trunk link: To demonstrate how this
Trunk to Access – Will It Work?
Recently a posted a question to Twitter about connecting two Cisco Catalyst switches. One switch has already booted and has the following configuration: The other switch is connected to Gi1/0/48 and has just been powered on. It has no configuration
STP Notes for CCDE
These are my study notes for CCDE based on “CCIE Routing and Switching v5.0 Official Cert Guide, Volume 1, Fifth Edition” and “Designing Cisco Network Service Architectures (ARCH) Foundation Learning Guide: (CCDP ARCH 642-874), Third Edition“, “INE – Understanding MSTP”
Ethernet, STP, Topology change and the behaviour of Ethernet
Introduction This post is inspired by a post at IEOC about Uplinkfast and TCN which can be found here. Before we get to those parts, let’s recap how Ethernet and STP work together. Spanning Tree The Spanning Tree Algorithm builds
RSTP synchronization – behind the scenes
RSTP synchronization is not widely understood and often oversimplified. This post describes how it really works in detail to give you the full picture.
Busting myths – Spanning tree portfast on the interface
I would like to bust a common myth. One that I’m probably guilty of preaching before as well. We all know that when portfast is enabled the port will bypass the listening and learning phase of STP. Portfast can be
I’m doing two lectures at Cisco Learning Network on spanning tree
Hi guys, I am going to be doing two lectures on spanning tree over at the Cisco Learning Network. The first one will be aimed for CCNA level plus and the second one will be aimed for CCNP level plus.
STP convergence – MST
In the comments I received a wish to compare RPVST+ with MST. RPVST+ is Ciscos proprietary STP running one instance per VLAN over 802.1Q trunks. MST is an industry standard which can run multiple instances but not one per VLAN.
Spanning tree convergence
Someone asked the other day how fast STP converges depending on PVST+ or RPVST+ or MST is running. Usually the answer for PVST+ is 30-50 seconds and for RPVST+ it’s fast, maybe less than a second. I thought I would