RPVST and PVST in cisco switch

[13jobsp90]

I have a core switch 4506 model running on PVST and new cisco switch 3850 model which I have to connect to that core switch through trunk line which is running on RPVST mode. Will there be any issue or problem connecting both since both are different STP modes?

[balaji.bandi]

They work normal way, but if you looking to get RPVST feature suggest to run both same as possible :

https://www.cisco.com/c/en/us/support/docs/lan-switching/spanning-tree-protocol/24062-146.html

[13jobsp90]

will there be any issue?

[balaji.bandi]

as i mentioned i do not see they can be co-exits if that is requirement, for better outcome when you get change move to RPVTS is suggested for fast convergency and other advantage which RPVST carry.

[MHM Cisco World]

There is no problem at all.

I will share with you lab connect two SW different modes 

MHM

[13jobsp90]

I tried to ask this question to chat gpt, they said it is better to normalize all the SWS in same STP mode  because it causes loops or network stablility issues.

[Joseph W. Doherty]

Take any ChatGPT info with a large grain of salt, especially when the question is "nuanced" or a subtle "it depends".

These AIs are still subject to GIGO (garbage in, garbage out).  Basically they are "trained" by lots of data, but is all that data correct or complete?  Or, what about contradictory?

About a year ago, I obtained a ChatGPT account, to try it myself.  I was very impressed how my questions were understood, and some of the factual data quicky presented, but when I started to ask expert level questions, ChatGPT's answers didn't correctly answer them.

IMO, ChatGPT, was a great Idiot Savant, across multiple subjects, but I didn't see much, if any, intelligence along the lines of reasoning.

What I observed, also, I believe, goes far in explaining some of the notable. AI "failures" that have been published.

BTW, don't take the forgoing as being against using something like ChatGPT, just understand its pluses and minuses.

[MHM Cisco World]

[13jobsp90]

Briefly I will explain my network infra. 

Core switch and it is connected to a distribution switch and from distribution it goes to several access switches with cascaded connection. Several other farm switches are connected to this core switch but all these (including core,distribution,access) switches are currently running  on PVST. This new server switch  which I am going to connect directly to core switch is 3850 model which came by default with RPVST mode.So when I connect directly to Core SW, will any issues happens (like loop or anything else) to other switches which are operational. 

[13jobsp90]

Pls update your result..

[Joseph W. Doherty]

They should interoperate (which should be shown when @MHM Cisco World posts his lab results).  However, would recommend (as does @balaji.bandi ) PVST be migrated to rapid-PVST, it's better for multiple reasons, and when you mix the two, you drag the rapid-PVST down to the PVST standard.

[13jobsp90]

how come RPVST goes down to PVST until or unless we change through command?

[Joseph W. Doherty]

Unsure I understand your question.

Does "goes down" refer to temporary or permanent failure, or reduction to common features?

[13jobsp90]

what he meant by that?I didnt get it..

[paul driver]

Hello
IF the current core switch is configured correctly to accept that new switch even if its running stp pvst+ or rstp then it would not cause any disruption

To give you ease of mind the most simplistic solution would be to change the new switch to stp mode to pvst+ but you still need to make sure the core switch vlan priority's (bridge ID) will not be superseded or the vtp database overwritten (if vtp is active) by that new switch addition.

New switch ( before addition to production network)
conf t
vtp mode transparent
vtp mode client
spanning-tree mode pvst
spanning-tree uplinkfast ( just on access-switches)
spanning-tree portfast edge default
spanning-tree portfast edge bpduguard
spanning-tree backbonefast ( if enabled on all switch's)
spanning-tree vlan 1-4094 priority 61440