Rapid Pvst+ Interoperation With Legacy 802.1D Stp; Rapid Pvst+ Interoperation With 802.1S Mst; Configuring Rapid Pvst - Cisco Nexus 3000 series Configuration Manual

Configuring Rapid PVST+

Rapid PVST+ Interoperation with Legacy 802.1D STP

Rapid PVST+ can interoperate with switches that are running the legacy 802.1D protocol. The switch knows
that it is interoperating with equipment running 802.1D when it receives a BPDU version 0. The BPDUs for
Rapid PVST+ are version 2. If the BPDU received is an 802.1w BPDU version 2 with the proposal flag set,
the switch sends an agreement message after all of the other ports are synchronized. If the BPDU is an 802.1D
BPDU version 0, the switch does not set the proposal flag and starts the forward-delay timer for the port. The
new root port requires twice the forward-delay time to transition to the forwarding state.
The switch interoperates with legacy 802.1D switches as follows:
• Notification—Unlike 802.1D BPDUs, 802.1w does not use TCN BPDUs. However, for interoperability
• Acknowledgement—When an 802.1w switch receives a TCN message on a designated port from an
This method of operation is required only for 802.1D switches. The 802.1w BPDUs do not have the TCA bit
set.
• Protocol migration—For backward compatibility with 802.1D switches, 802.1w selectively sends 802.1D
When a port is initialized, the migrate-delay timer is started (specifies the minimum time during which 802.1w
BPDUs are sent), and 802.1w BPDUs are sent. While this timer is active, the switch processes all BPDUs
received on that port and ignores the protocol type.
If the switch receives an 802.1D BPDU after the port migration-delay timer has expired, it assumes that it is
connected to an 802.1D switch and starts using only 802.1D BPDUs. However, if the 802.1w switch is using
802.1D BPDUs on a port and receives an 802.1w BPDU after the timer has expired, it restarts the timer and
starts using 802.1w BPDUs on that port.
If you want all switches to renegotiate the protocol, you must restart Rapid PVST+.
Note

Rapid PVST+ Interoperation with 802.1s MST

Rapid PVST+ interoperates seamlessly with the IEEE 802.1s Multiple Spanning Tree (MST) standard. No
user configuration is needed.
Configuring Rapid PVST+
Rapid PVST+, which has the 802.1w standard applied to the Rapid PVST+ protocol, is the default STP setting
in the software.
with 802.1D switches, Cisco NX-OS processes and generates TCN BPDUs.
802.1D switch, it replies with an 802.1D configuration BPDU with the TCA bit set. However, if the
TC-while timer (the same as the TC timer in 802.1D) is active on a root port connected to an 802.1D
switch and a configuration BPDU with the TCA set is received, the TC-while timer is reset.
configuration BPDUs and TCN BPDUs on a per-port basis.
Cisco Nexus 3000 Series NX-OS Layer 2 Switching Configuration Guide, Release 5.0(3)U1(1)
Rapid PVST+ Interoperation with Legacy 802.1D STP
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