Planet IGS-801 [69/120] User s manual of igs 801m
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Planet IGS-801 [69/120] User s manual of igs 801m

User’s Manual of IGS-801M
Bridge Protocol Data Units
e following information is used:
The unique switch identifier
ost to the root associated with each switch port
entifier
The path cost to the root from the transmitting port
n
Us are not directly forwarded by the switch, but the receiving
switch uses the information in the frame to calculate a BPDU, and, if the topology changes, initiates a BPDU transmission.
e
e root.
A port for each switch is selected. This is the port providing the best path from the switch to the root switch.
ork. This propagation delay can result in topology changes where a
port that transitioned directly from a Blocking state to a Forwarding state could create temporary data loops. Ports must
ard packets. They
for w the network topology to stabilize after a topology change. In addition, STP specifies a
chan
Each port on a switch using STP exists is in one of the following five states:
Blocking – the port is blocked from forwarding or receiving packets
For STP to arrive at a stable network topology, th
The path c
The por tid
STP communicates between switches on the network using Bridge Protocol Data Units (BPDUs). Each BPDU contains
the following information:
The unique identifier of the switch that the transmitting switch currently believes is the root switch
The port identifier of the transmitting port
The switch sends BPDUs to communicate and construct the spanning-tree topology. All switches connected to the LAN o
which the packet is transmitted will receive the BPDU. BPD
The communication between switches via BPDUs results in the following:
One switch is elected as the root switch
The shortest distance to the root switch is calculated for each switch
A designated switch is selected. This is the switch closest to the root switch through which packets will b
forwarded to th
Ports included in the STP are selected.
Creating a Stable STP Topology
It is to make the root port a fastest link. If all switches have STP enabled with default settings, the switch with the lowest
MAC address in the network will become the root switch. By increasing the priority (lowering the priority number) of the
best switch, STP can be forced to select the best switch as the root switch.
When STP is enabled using the default parameters, the path between source and destination stations in a switched
network might not be ideal. For instance, connecting higher-speed links to a port that has a higher number than the
current root port can cause a root-port change.
STP Port States
The BPDUs take some time to pass through a netw
wait for new network topology information to propagate throughout the network before starting to forw
must also wait for the packet lifetime to expire for BPDU packets that were forwarded based on the old topology. The
ward delay timer is used to allo
series of states a port must transition through to further ensure that a stable network topology is created after a topology
ge.
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