Protocol Timers - Cisco AJ732A - MDS 9134 Fabric Switch Configuration Manual

Chapter 8 Configuring 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
Figure 8-4
Switch A
DP = designated port
RP = root port
F = forwarding
Switch A sends a proposal message (a configuration BPDU with the proposal flag set) to switch B,
proposing itself as the designated switch (see
After receiving the proposal message, switch B selects as its new root port the port from which the
proposal message was received, forces all non-edge ports to the blocking state, and sends an agreement
message (a BPDU with the agreement flag set) through its new root port.
After receiving the agreement message from switch B, switch A also immediately transitions its
designated port to the forwarding state. No loops in the network can form because switch B blocked all
of its non-edge ports and because there is a point-to-point link between switches A and B. (See the
States" section on page 8-11
When switch C connects to switch B, a similar set of handshaking messages are exchanged. Switch C
selects the port connected to switch B as its root port, and both ends of the link immediately transition
to the forwarding state. With each iteration of this handshaking process, one more network device joins
the active topology. As the network converges, this proposal-agreement handshaking progresses from the
root toward the leaves of the spanning tree.
The switch learns the link type from the port duplex mode: a full-duplex port is considered to have a
point-to-point connection and a half-duplex port is considered to have a shared connection. You can
override the default setting that is controlled by the duplex setting by entering the spanning-tree
link-type interface configuration command.
This proposal/agreement handshake is initiated only when a non-edge port moves from the blocking to
the forwarding state. The handshaking process then proliferates step-by-step throughout the topology.

Protocol Timers

Table 8-2
OL-16597-01
Proposal and Agreement Handshaking for Rapid Convergence
Proposal
Root
Agreement
F
DP RP
Root
F
DP RP
Root
F
DP RP
for information on port states.)
describes the protocol timers that affect the Rapid PVST+ performance.
Switch B
Designated
switch
F
Designated
switch
Proposal
F
Designated
switch
Agreement
F F
DP
Figure 8-4).
Cisco Nexus 5000 Series Switch CLI Software Configuration Guide
Information About Rapid PVST+
Switch C
F
RP
"Port
8-9