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Figure 27 BPDU processing in RSTP
PVST
In an STP- or RSTP-enabled LAN, all bridges share one spanning tree. Traffic from all VLANs is
forwarded along the spanning tree, and ports cannot be blocked on a per-VLAN basis to prune loops.
PVST allows every VLAN to have its own spanning tree, which increases usage of links and
bandwidth. Because each VLAN runs RSTP independently, a spanning tree only serves its VLAN.
A PVST-enabled H3C device can communicate with a third-party device that is running Rapid PVST
or PVST. The PVST-enabled H3C device supports fast network convergence like RSTP when
connected to PVST-enabled H3C devices or third-party devices enabled with Rapid PVST.
PVST protocol frames
As shown in
, a PVST BPDU uses the same format as an RSTP BPDU except the following
differences:
•
The destination MAC address of a PVST BPDU is 01-00-0c-cc-cc-cd, which is a private MAC
address.
•
Each PVST BPDU carries a VLAN tag. The VLAN tag identifies the VLAN to which the PVST
BPDU belongs.
•
The organization code and PID fields are added to the LLC header of the PVST BPDU.
Figure 28 PVST BPDU format
A port's link type determines the type of BPDUs the port sends.
•
An access port sends RSTP BPDUs.
•
A trunk or hybrid port sends RSTP BPDUs in the default VLAN and sends PVST BPDUs in other
VLANs.