Luxul XMS-1024P - Manual (Page 94)

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XMS-1024P
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LUX-UG-XMS-1024P Vers: 081314
Step Operation
2 Using the Root Port BPDU and the Root Path cost, the Switch generates a Designated
Port BPDU for each of its Ports.
„
Root ID is replaced with that of the Root Port;
„
Root Path is replaced with the sum of the Root Path cost of the root Port and the
path cost between this Port and the Root Port;
„
The ID of the Designated Bridge is replaced with that of the Switch;
„
The ID of the Designated Port is replaced with that of the Port.
3 The Switch compares the resulting BPDU with the BPDU of the desired Port whose role
is yet to be determined.
„
If the resulting BPDU takes precedence over the BPDU of the Port, the Port is
chosen as the Designated Port and the BPDU of this Port is replaced with the
resulting BPDU.
„
If the BPDU of this Port takes precedence over the resulting BPDU, the BPDU of this
Port is not replaced and the Port is Blocked. The Port can now only receive BPDUs
and will not process any other traffic.
Table 7-2 Selecting root Port and designated Port
NOTE: In an STP Network with a stable topology, only the Root Port(s)
and Designated Port(s) can forward Data, the other Ports are
Blocked. Blocked Ports only can receive BPDUs and will not
process any other traffic.
RSTP (Rapid Spanning Tree Protocol) evolved from the 802.1D STP standard, and enables
Ethernet Ports to change their states rapidly. The premise for Ports in RSTP to change
states rapidly are as follows.
The condition needed for the Root Port to change its Port state rapidly: The previous
Root Port of the Switch stops forwarding Data and the Designated Port of the upstream
Switch begins to forward Data.
The condition needed for the Designated Port to change its Port state rapidly: The
Designated Port is an edge Port or connected to a point-to-point link. If the designated
Port is an edge Port, it can directly change to a forwarding state. If the Designated Port
is connected to a point-to-point link, it can change its forwarding state after receiving a
response from the downstream Switch through a handshake.
RSTP Enhancements
Edge Port: Indicates a Port connected directly to a Layer 3 device such as a Router.
P2P Link: Indicates a link between two directly connected Switches.