On an 802.1q trunk, the PVST+ enabled switch sends the following BPDUs:
For all tagged VLANs on the port on which PVST+ is enabled, 802.1q tagged SSTP BPDUs are sent to the Cisco or Extreme MAC address. The 802.1q tag contains the VLAN ID. (VLAN 1 could be tagged on the port. In that case a tagged BPDU for VLAN 1 is sent). The IEEE compliant switches do not consider these BPDUs as a control packet. So they forward the frame as they would forward to any unknown multicast address on the specific VLAN.
If PVST+ is enabled on the untagged (native) VLAN of the port, an untagged SSTP BPDU is sent to the Extreme or Cisco MAC address on the native VLAN of the trunk. It is possible that the native VLAN on the Extreme or Cisco port is not VLAN 1. This BPDU is also forwarded on the native VLAN of the IEEE 802.1q switch just like any other frame sent to an unknown multicast address.
In addition to the above SSTP BPDUs, a standard IEEE BPDU (802.1d) is also sent, corresponding to the information of VLAN 1 on the Extreme or Cisco switch. This BPDU is not sent if VLAN 1 is explicitly disabled on the trunk port.
The following table lists the types of BPDUs sent in case of different port types. The numbers in the third column are the VLAN instance for which these BPDUs are sent/processed.
| Port Configuration | Extreme or Cisco - PVST(+) | VLAN instance |
|---|---|---|
|
Access - VLAN 1 |
Standard IEEE BPDU (64B) |
1 |
|
Access - VLAN 100 |
Standard IEEE BPDU (64B) |
100 |
|
Trunk - Native VLAN 1 Allowed VLANs - 1, 100, 200 |
Standard IEEE BPDU (64B) Extreme or Cisco untagged BPDU (68B) Extreme or Cisco tagged BPDU (72B) Extreme or Cisco tagged BPDU (72B) |
1 1 100 200 |
|
Trunk - Native VLAN 100 Allowed VLANs - 1, 100, 200 |
Standard IEEE BPDU (64B) Extreme or Cisco untagged BPDU (68B) Extreme or Cisco tagged BPDU (72B Extreme or Cisco tagged BPDU (72B) |
1 100 1 200 |
|
Trunk - Native VLAN 100 Allowed VLANs - 100 |
Extreme or Cisco untagged BPDU (68B) |
100 |
|
Trunk - Native VLAN 100 Allowed VLANs - 100, 200 |
Extreme or Cisco untagged BPDU (68B) Extreme or Cisco tagged BPDU (72B) |
100 200 |