Dell BigIron RX Series, Configuration Manual

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364 BigIron RX Series Configuration Guide
53-1002253-01
State machines
13
•
Proposing – The Designated port on the root bridge sends an RST BPDU packet to its peer port
that contains a proposal flag. The proposal flag is a signal that indicates that the Designated
port is ready to put itself in a forwarding state (
Figure 43 ). The Designated port continues to
send this flag in its RST BPDU until it is placed in a forwarding state ( Figure 46 ) or is forced to
operate in 802.1D mode. (Refer to “Compatibility of RSTP with 802.1D” on page 384)
•
Proposed – When a port receives an RST BPDU with a proposal flag from the Designated port
on its point-to-point link, it asserts the Proposed signal and one of the following occurs
(
Figure 43 ):
•
If the RST BPDU that the port receives is superior to what it can transmit, the port
assumes the role of a Root port. (Refer to
“Bridges and bridge port roles” on page 357.)
•
If the RST BPDU that the port receives is inferior to what it can transmit, then the port is
given the role of Designated port.
NOTE
Proposed will never be asserted if the port is connected on a shared media link.
In Figure 43 , Port3/Switch 200 is elected as the Root port
FIGURE 43 Proposing and proposed stage
•
Sync – Once the Root port is elected, it sets a sync signal on all the ports on the bridge. The
signal tells the ports to synchronize their roles and states (
Figure 44 ). Ports that are non-edge
ports with a role of Designated port change into a discarding state. These ports have to
negotiate with their peer ports to establish their new roles and states.
Switch 100
Root Bridge
Switch 200
Switch 300
Switch 400
Port2
Designated port
Proposing
Port1
Root port
Proposed
Port2
Port2
Port3
Port3
RST BPDU
sent with a
Proposal
flag