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PVSTP and RSTP compatibility

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David B. P.
Advisor

PVSTP and RSTP compatibility

Hello,
I have two 3400 switches where I have to connect two links to a customer which switches are running PVSTP. My switches are running RSTP. Do you know if it will work? Do you have any kind of experience? I am not very confident that they will understand each other and work fine.

Thanks.
3 REPLIES
Case Van Horsen
Frequent Advisor

Re: PVSTP and RSTP compatibility

If there is only a single, untagged VLAN on the link to the customer, it should work okay. If there are tagged VLANs on the link (even just one tagged VLAN), you'll encounter some issues.

RSTP sends its BPDUs untagged. Assuming tagging is active, they will be mapped to the "native" VLAN on the PVSTP switch. Since no BPDUs arrive on the tagged VLANs, the PVSTP switch typically just activate those VLANs. So it may appear to work or it may cause a broadcast storm.

casevh

Sietze Reitsma
Respected Contributor
Solution

Re: PVSTP and RSTP compatibility

Case Van Horsen
Frequent Advisor

Re: PVSTP and RSTP compatibility

Just a comment regarding the white paper from HP.

With recent versions of IOS, even if a Cisco switch is configured for MSTP, it listens for PVST BPDUs and will shutdown any ports that receive a PVST BPDU. You can have an MSTP based, correctly configured HP core with Cisco edge switches, and a single mis-configured(1) Cisco switch can shut down every other Cisco switch.

casevh

(1) All that is required is PVST or RPVST and 802.1q trunking on the uplink.