Understanding Spanning-Tree Port-Priority

In this video we will learn about the spanning-tree protocol port priority. We will examine the spanning-tree root bridge election process, root port and designated port election process and talk about how port-priority relates to these various elections.

We will look at an example on real Cisco gear and show you how to manipulate port-priority in such a way that will help you understand it's purpose thoroughly

Category:

Education

Tags:

• CCNA
• CCNP
• CCIE
• Cisco
• spanning-tree
• port-priority

[bagojunk2]

There are several REASONS why professional recordings are performed in studios with voice actors who take and retake segments, use noise filters, etc and among those reasons is MANY people do NOT want to hear lip smacking or slurping noises, heavy breathing cause you smoke or your lungs are otherwise constricted, or the residual saliva or phlegm in your mouth when you make your hard Cs in words like "cost". I wish I could have watched this whole video but I cannot as I am utterly disgusted.

[astorinonetworks]

@bagojunk2 Solution: don't watch the video and go learn STP from somebody else.

[astorinonetworks]

Part of what you said is right : ) -- Changing the port-priority on Cat2 fa0/24 will not change anything. It will not make Cat2 Fa0/24 the root port of Cat2. You would have to change port-priority on Cat1 Fa0/24 as I did in the video to make that happen.

On Cat2 if you have fa0/23 the root port for VL2 and F0/24 the root for VL6 then yes you could do what you are talking about.  To make that happen though you either need to change port-priority on Cat1 or spanning-tree port cost on Cat2

[fumega]

(2)

unchanged, than we would have the Fa0/24 of Cat2 being the root for Vlan 2 and Fa0/23 being the root for Vlan 1 right? This design would allow more bandwidth per Vlan.

[astorinonetworks]

@fumega You can do that to enable a type of load-balancing but you are not adding more bandwidth per vlan. You still have 1 interface forwarding and 1 interface blocking per VLAN.

If I leave the defaults I have Fa0/23 forwarding and Fa0/24 blocking for both VLANs. If we change the port-priority of Fa0/24 of Cat1 for only VLAN 2 you would have Fa0/23 forwarding for VLAN 1 and blocking for VLAN2 and Fa0/24 blocking for VLAN1 and forwarding for VLAN2 on Cat2

[TsirosProductions]

What font and font size do you use for your terminal settings?

[fumega]

@astorinonetworks

2 only for vlan 1. So every Vlan would have its own 1Gb/s port vs 1Gb/s shared port.

I don't know if this works in production, that why I'm asking ;-)

Regards.

[fumega]

@astorinonetworks

1Hi Astorino.

First thank you for you fast reply.

When I said that we would have more bandwidth per Vlan, I was referring to the fact that with the default STP port Fa0/24 on CAT2 would be blocked for all Vlans, and Fa0/23 would be the forwarding for all vlans (root). So if we changed the priority for Vlan, let's say, 6, on Fa0/24 of CAT2, Fa0/24 would become the root of CAT2, and Fa0/23 would be ALTN blocked for Vlan6. So we would have the Fa0/24 only for Vlan6 and Fa0/23

[fumega]

(1) Hello.

I've just discovered your website and Youtube videos, they're amazing!

By the way, we can take advantage of this feature in order to increase the available bandwidth per Vlan right? For instance, if there were two vlans, 1 and 2, by default all switches would have the same forwarding and blocking ports for all vlans. But if we changed the port-priority of VLan 2 on Fa0/24 of CAT 1 to, let's say, 32 (spanning-tree vlan 5 port-priority 32) and left the vlan 1 port priority