Pvstp+

BroadcastStorm

I just wanted to share my notes in regards to PVSTP+ please give me your feedback if I understood this correctly.

Per VLAN Spanning Tree + (PVST+)

The concept behind PVSTP is that a specific VLAN will have it's forwarding links (active links), and block some of the links to avoid loop, but also allow other vlan traffic on this blocked link.

VLAN 10 (switch 1), while Switch 2 and Switch 3 link to Switch 1 is set to forwarding (way to reach the root bridge), links between Switch 2 and 3 is set to blocking which is typical in a STP algorithm to avoid loop.

But this is where the part it gets very interesting, VLAN 20 (switch 2) direct link with Switch 1 and Switch 3 will be set to forwarding while direct link between Switch 1 and Switch 3 will be set to blocking.

This concept is confusing, but imagine the link as hybrid, and allows only certain traffic, a good analogy is a road A only allows trucks to pass and blocks cars, while road B does the opposite which allows cars to pass, but blocks trucks.
With this concept, no links is wasted.
vlan10 VLAN20
SW1

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SW2
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* +
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SW3

The diagram s a triangle 3 switches has connection to each other, the text diagram won't stick.

networker050184

BroadcastStorm wrote: »

The diagram s a triangle 3 switches has connection to each other, the text diagram won't stick.

Use the code tags to retain formatting.

One thing I'm not sure if you understand or just didn't put in your notes, is that the load balancing functions are not by default. The switches will not automatically block for some VLANs and forward for others unless you tell it too. If left to defaults all VLANs will choose the same root and forward across the same links.