Information About Rapid PVST+
S e n d f e e d b a c k t o n x 5 0 0 0 - d o c f e e d b a c k @ c i s c o . c o m
The TCA flag is used only when the switch is interacting with switches that are running legacy 802.1D
Note
STP. See the
information about Rapid PVST+ interaction with 802.1D STP.
The proposal and agreement sequence then quickly propagates toward the edge of the network and
quickly restores connectivity after a topology change (see the
on page
Rapid PVST+ BPDUs
Rapid PVST+ and 802.1w use all six bits of the flag byte to add the role and state of the port that
originates the BPDU, and the proposal and agreement handshake.
flags in Rapid PVST+.
Figure 8-3
0
Proposal
Topology change
Another important change is that the Rapid PVST+ BPDU is type 2, version 2, which makes it possible
for the switch to detect connected legacy (802.1D) bridges. The BPDU for 802.1D is version 0.
Proposal and Agreement Handshake
As shown in
ports are in the blocking state. Assume that the priority of switch A is a smaller numerical value than the
priority of switch B.
Cisco Nexus 5000 Series Switch CLI Software Configuration Guide
8-8
"Rapid PVST+ Interoperation with Legacy 802.1D STP" section on page 8-16
8-13).
Rapid PVST+ Flag Byte in BPDU
1
2
3
4
5
Agreement
Forwarding
Learning
Port role
Figure
8-4, switch A is connected to switch B through a point-to-point link, and all of the
6
7
Topology change ACK
00 Unknown
01 Alternate/Backup
02 Root
11 Designated
Chapter 8
Configuring Rapid PVST+
"Synchronization of Port Roles" section
Figure 8-3
shows the use of the BPDU
for
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