PVSTP+ is an improved version of the Cisco proprietary Spanning Tree protocol PVST that runs an instance of STP per VLAN. The main difference between PVST and PVST+ is that PVST+ provides support for compatibility with other STP versions and operates over 802.1Q trunks as well as ISL Trunks. Running an STP instance per VLAN gives you the ability to not only fine tune the STP tree based on where VLANs are in use, but also load balance VLANs across multiple Root Bridges.
Spanning Tree is a mechanism for Layer 2 switches to prevent switching loops over redundant switch links. Switches learn about other switches in the network and the ports they are connected to by sending out Bridge Protocol Data Units (BPDU), advertising STP information. These BPDUs are used to determine which switch ports should forward traffic and which switch ports should block traffic. In a simple 3 Switch topology as shown below, SW1 connects to SW2 on G1/0/2 and SW3 on G1/0/3, SW2 Connects to SW1 on G1/0/1, and SW3 on G1/0/3, and SW3 Connects to SW1 on G1/0/1 and SW2 on G1/0/2.
When a network device forwards data there are only 2 options other than if the data is destined locally:
- Forwarding data on the same subnet
- Forwarding data on a different subnet.
The CAM Table
Let's talk about how we connect devices to our networks and how we segment these networks. Well physically at least. This post isn't about WiFi.
Let's start with the basics of how Network engineers explain how data traverses the network. When you click on the browser, or open a web page, or send an email on your PC, data is send over the network medium whether it be via copper, fiber, or wireless. At it's most basic form, all data is sent as little electrical pulses of 1's or 0's. But how does that web page go from words and pictures and CSS etc to those 1's and 0's? The answer of course is Data Encapsulation/Decapsulation.
So like many others (I'm hoping I wasn't the only one at least) I let my Cisco certifications expire during COVID. Partially because I wasn't ready to redo any of the CCNP exams, although I probably could have done the TSHOOT exam, and partially because I was lazy and COVID was here and it was too hard. That was back in 2019 and now I have no current Cisco certifications.