Proxim ORiNOCO AP-800 Installation And Management Manual page 41

b. Listening: When STP is enabled, the AP devices exchange Bridge Protocol Data Unit (BPDU) packets in listening state.
These BPDU packets contain the Bridge Priority and MAC Address information, based on which a root bridge and
Designated Bridge are selected.
• Root Bridge: It is the device that determines the shortest low cost path to forward the data, by blocking
alternate high cost paths and avoiding loops on the network. Root bridge has the lowest MAC Address or
highest priority and transmits the network topology information continuously to other bridges on the network.
• Designated Bridge: It is the device closest to the Root Bridge and is responsible for forwarding the data
towards the root. All the other devices in the network other than Root Bridge, act as Designated Bridge.
c. Learning: Once the Root Bridge and Designated Bridge are selected, all the devices learn and update the Bridge
Priority and MAC address information in their learn table. The Root bridge updates the learn table and finds the
shortest low cost path in the bridged network, to forward packets.
d. Blocking: After selecting the low cost path, the device blocks and disables all the other high cost paths active in other
interfaces. Once the path is blocked, no traffic is allowed via that high cost path.
e. Forwarding: The device easily forwards the data packet to the destination via single low cost path, with zero loops
and interference in bridge network.
: The state of the port must change from blocking state to listening and learning state, before it can change to
the forwarding state.
Following figure and explanation illustrates the work process of STP in detail:
•
Let us consider a network with three Bridges (Bridge 1, Bridge 2 and Bridge 3). Bridge 1 and Bridge 2 are connected
via both Wireless and Ethernet interface, while Bridge 3 is connected to Bridge 1 and Bridge 2 only via Wireless
interface.
ORiNOCO® AP-800 and AP-8000 Installation and Management Guide
Figure 3-6 STP Topology
Device Configuration Using Web Interface
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