Should a BPDU on VLAN 1 instance always be sent in PVST+ ?

[gyeongcheollee]

Hi.

I have some issue understanding the exact operation of PVST+ especially about transmission of BPDUs on VLAN 1.

Does a PVST+ switch always send BPDUs on VLAN 1 even if the port is not set for the VLAN 1?

The following articles say that VLAN 1 is used to interoperate with the conventional STP. To my understanding, if that's true, the instance for VLAN 1 shall not be removed and the BPDUs for VLAN 1 shall be sent or received to interoperate the conventional STP.

https://traceroute.home.blog/category/spanning-tree/per-vlan-spanning-tree-pvst/

https://learningnetwork.cisco.com/s/question/0D53i00000Kt1f1CAB/pvst-and-common-stp-native-vlan-operations

https://docs.commscope.com/bundle/fastiron-08095-l2guide/page/GUID-B9E37883-B822-4642-9412-0308D56F6BDF.html

https://community.cisco.com/t5/switching/how-bpdu-is-transmitted-with-native-vlan-for-pvst-and-mstp/td-p/1631995

The following Cisco articles say that untagged STP(IEEE 802.1Q) BPDUs are received on the port's PVID, but I guess that doesn't fully contradict my understanding. The STP BPDUs may be sent or received on the port's PVID, but PVST BPDUs tagged by VLAN 1 may be sent anyway, even if the PVID is not VLAN 1.  

https://www.cisco.com/en/US/docs/ios/lanswitch/configuration/guide/lsw_rtng_vlan_ovw_ps6350_TSD_Products_Configuration_Guide_Chapter.html#wp1006501

https://www.cisco.com/c/en/us/support/docs/lan-switching/spanning-tree-protocol/24063-pvid-inconsistency-24063.html

My questions are following:

1. Is it possible that a PVST+ switch doen't send any BPDU on VLAN 1, if the PVID of the port is not VLAN 1?  

2. Does the STP(IEEE) BPDU have the information of the PVST+ instance for the VLAN that matches the PVID, not for VLAN 1?

3. If so, does the PVST+ switch interoperate with the conventional STP devices with the VLAN that matches the PVID? 

Thank you.

[MHM Cisco World]

let make it more clear here 
1- port is trunk 
here there are two behave when the vlan1 is native and when non vlan1 is native cisco list the different below 

 This list shows how PVST+ interoperates with IEEE 802.1Q or IEEE 802.1D, if the Native VLAN on an IEEE 802.1Q trunk is VLAN 1:

• VLAN 1 STP BPDUs are sent to the IEEE STP MAC address (0180.c200.0000), untagged.

• VLAN 1 STP BPDUs are also sent to the PVST+ MAC address, untagged.

• Non-VLAN 1 STP BPDUs are sent to the PVST+ MAC address (also called the Shared Spanning Tree Protocol (SSTP) MAC address, 0100.0ccc.cccd), tagged with a corresponding IEEE 802.1Q VLAN tag.

If the Native VLAN on an IEEE 802.1Q trunk is not VLAN 1:

• VLAN 1 STP BPDUs are sent to the PVST+ MAC address, tagged with a corresponding IEEE 802.1Q VLAN tag.

• VLAN 1 STP BPDUs are also sent to the IEEE STP MAC address on the Native VLAN of the IEEE 802.1Q trunk, untagged.

• Non-VLAN 1 STP BPDUs are sent to the PVST+ MAC address, tagged with a corresponding IEEE 802.1Q VLAN tag.

2- port is access 

the two SW the port config with vlan10 

you can see the STP send two bpdu 
one tag with VLAN10 
other not tag and since this is access not trunk port so this no tag bpdu is for vlan1 

MHM

[gyeongcheollee]

Thank you for answering my questions.

Let me describe what I understand by your answer. Am I correct?

If a port is a trunk port, then 

• VLAN 1 STP (IEEE) BPDUs are sent untagged.
• VLAN 1 PVST+ BPDUs are sent tagged (the native VLAN is not VLAN 1), or untagged (the native VLAN is VLAN 1)

If a port is an access-port, then

• VLAN 1 STP (IEEE) BPDUs are sent untagged.
• VLAN 1 PVST+ BPDUs are sent, if the port is set for VLAN 1.
• VLAN 1 PVST+ BPDUs are not sent, if the port is not set for VLAN 1.