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Slight confusion with STP

Maybe I'm just thinking too hard on this, trying to separate 802.1d / 802.1w in my head, and how the Cisco version play in to the standards.

So my question is mainly this: if we are using 802.1q, and Cisco devices default to PVST (IEEE), which only works with ISL, is STP actually even running in this situation?

Also, do I understand the standards correctly?

CST (STP, IEEE) - 802.1d (802.1q)
PVST - 802.1d (ISL)
PVST+ - 802.1d (802.1q)

RSTP - 802.1w (802.1q)
RPVST+ 802.1w (802.1q)

Is this correct?

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Networking Student2 points·3 months ago

From my Scaling Networks Companion Guide v6:

  • 802.1d is the original STP standard and is also known as CST (Common Spanning Tree). One spanning-tree instance for the entire bridged network, no matter how many vlans you have

  • 802.1d is the same standard for PVST+, which is the Cisco enhancement of the original STP, and allows a seperate spanning-tree instance for each vlan

  • 802.1w is the standard defined for Rapid STP (RSTP), and its only difference from the original STP is faster convergence

  • Rapid PVST+ is Cisco's enhancement of RSTP, therefore it uses the 802.1w standard as well

  • MSTP has the standard 802.1s

I couldn't exactly remember off the top of my head. You should get that book, it saved my life and helped me pass my practical + exam :D

Original Poster1 point·3 months ago

Right on thank you.
So it would appear the PVST isn’t part of a standard then, as it only inter operates with an ISL infrastructure

Networking Student1 point·3 months ago

I would imagine so, yeah

note that there is pvst and pvst+. pvst is the one that will only work with ISL, whereas PVST+ will work with 802.1q

That was a point of confusion for me to.

CCIE1 point·3 months ago

I can't believe isl is still taught, it's nowhere in real world environments

PracticalNetworking.net1 point·3 months ago

Seriously. Even modern Cisco switches don't support it anymore. =)

Networking Student1 point·3 months ago

this is what I've been thinking while going through some of the Cisco stuff. like, mention it sure but what's the point in anything more???

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