User`s manual

EDS-P510 Series Featured Functions
3-37
Bridge will flow through the Designated Bridge. The port on this bridge that connects to the segment is
called the Designated Bridge Port.
STP Configuration
After all the bridges on the network agree on the identity of the Root Bridge, and all other relevant parameters
have been established, each bridge is configured to forward traffic only between its Root Port and the
Designated Bridge Ports for the respective network segments. All other ports are blocked, which means that
they will not be allowed to receive or forward traffic.
STP Reconfiguration
Once the network topology has stabilized, each bridge listens for Hello BPDUs transmitted from the Root Bridge
at regular intervals. If a bridge does not receive a Hello BPDU after a certain interval (the Max Age time), the
bridge assumes that the Root Bridge, or a link between itself and the Root Bridge, has gone down. This will
trigger the bridge to reconfigure the network to account for the change. If you have configured an SNMP trap
destination, when the topology of your network changes, the first bridge to detect the change sends out an
SNMP trap.
Differences between RSTP and STP
RSTP is similar to STP, but includes additional information in the BPDUs that allow each bridge to confirm that
it has taken action to prevent loops from forming when it decides to enable a link to a neighboring bridge.
Adjacent bridges connected via point-to-point links will be able to enable a link without waiting to ensure that
all other bridges in the network have had time to react to the change. The main benefit of RSTP is that the
configuration decision is made locally rather than network-wide, allowing RSTP to carry out automatic
configuration and restore a link faster than STP.
STP Example
The LAN shown in the following figure has three segments, with adjacent segments connected using two
possible links. The various STP factors, such as Cost, Root Port, Designated Bridge Port, and Blocked Port are
shown in the figure.
Bridge A
LAN Segment 3
LAN Segment 2
LAN Segment 1
Port 2
(Root Bridge)
Port 1
(Designated
Bridge Port)
Bridge B
Port 2
(Designated
Bridge Port)
Port 1
(Root Port)
Cost =100
Bridge X
Port 2
(Blocked Port)
Port 1
(Root Port)
Cost =100
Bridge C
Port 2
(Designated
Bridge Port)
Port 1
(Root Port)
Cost =100
Bridge Y
Port 2
(Blocked Port)
Port 1
(Root Port)
Cost =200
• Bridge A has been selected as the Root Bridge, since it was determined to have the lowest Bridge Identifier
on the network.