Administrator Guide

Spanning Tree Protocol 795
Figure 22-7. RSTP-PV and RSTP Interoperability
SW3 sends IEEE STP BPDUs to the IEEE multicast MAC address as
untagged frames. These BPDUs are processed by the VLAN 1 STP instance
on the RSTP-PV switch as part of the VLAN 1 STP instance.
The RSTP-PV side sends IEEE STP BPDUs corresponding to the VLAN 1
STP to the IEEE MAC address as untagged frames across the link. At the
same time, SSTP BPDUs are sent as untagged frames. IEEE switches simply
flood the SSTP BPDUs throughout VLAN 1. This facilitates RSTP-PV
connectivity in case there are other RSTP-PV switches connected to the IEEE
STP domain.
For non-native VLANs (VLANs 2–4093), the RSTP-PV switch sends SSTP
BPDUs, tagged with their VLAN number. The VLAN STP instances are
multicast across the RSTP region, as if it were a hub switch.
SW1 SW2
SW3
1/0/1 1/0/1
1/0/2
1/0/3
1/0/4
Root for VLAN1
1/0/1
Root for VLAN2 and 3
VLAN1
VLAN2
VLAN3