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Rapid-PVST probleme


We have migrate the LAN from PVST to Rapid-PVST yesterday. But now, some switch can non longer be joinable...

PLAN: 2950T (12.1.19.EA1C) with rpvst enable but with no vlan enable "no spann vlan 1 , same for all vlan), are connected to 2950C (12.1.19.EA1C) with rpvst enable on all vlan.

All 2950C are connected to 3550 with rpvst enalbe for all vlan with vtp version 1.

Question1: must i enable all vlan on 2950T ? (i do not do this before, because of the diameter of STP)

Question2: must i make interface trunk between 2950T and C in portfast mode ? (this for no stp waiting for these port when other on the same switch interface changing state).


Re: Rapid-PVST probleme

Normally Portfast mode is configured on nontrunking ports .Spanning tree loops can occur if BPDUs are still being transmitted and received on nontrunking switch ports.Its good to enable all Vlans on 2950T.For more information refer the following URL

Re: Rapid-PVST probleme

Hi Maxime,

I expect your network to be a little bit more complex than what you described if you had to disable STP because of diameter issues;-)

Q1: regardless of the STP mode, I would recommend keeping STP on all your switches. The diameter problems are very often over-rated (you need to really have a large network to be concerned about diameter. The advertised limit of 7 is very conservative for the diameter).

Q2: on the 2950T with no STP, portfast would have no effect anyway. It would probably be a configuration error to add it on the side of the 2950C that sees the 2950T as a plain hub. Anyway, portfast would probably not help if you have a permanent loss of connectivity.

Generally speaking, I don't see what difference between PVST and rapid-PVST could lead to a loss of connectivity. They both work in a very similar way and reach the same "conclusions" as to the role and state of the ports. It's just the transitions between the different states that are different (and faster with rapid-PVST).

Do you think that you are experiencing a bridging loop? Else, try to focus on one particular switch that you cannot reach, and check the STP status on the ports on the path to this switch.



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Re: Rapid-PVST probleme


In the network, i have enable RPVST on all 2950T switch. And it is good now. I think that :

When a port (with PC for example) on the 2950C (where the 2950T is connected too) goes up, the 2950C make all the port in non PortFast mode down for 4 seconde anyway. But the physical layer do not see this disconnecting probleme. It is a RPVST process and there is nothing in the log.

I dont understand why but this is the reality.

And when the supervision station try to ping the 2950T durring theses second... the map goes red because of this disconnecting.

But enable RPVST on all vlan of all 2950T in my network resolve this probleme.

WARNING: Probleme encounter in the old 3Com switch where portfast is disable. Sometime these 3Com switch goese down like 2950T before activating RPVST...

I think to enable portfast on these ports (to 3Com switch) to resolv this probleme.

Thank you all for help.

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