D-Link DES-7000 Series, Руководство пользователя

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DES-7000/DES-7100 Layer 2 Switch User
’
s Guide
Switch Management
36
Switch Level STP
The user may configure the switch STP parameters listed here:
Parameter Description Default Value
Bridge Identifier
(Not user-
configurable
except by setting
priority below)
A combination of the User-set priority and the
switch
’
s MAC address. The Bridge Identifier
consists of two parts: a 16-bit priority and a
48-bit Ethernet MAC address
32768 + MAC
Priority
A relative priority for each switch
–
lower
numbers give a higher priority and a greater
chance of a given switch being elected as the
root bridge
32768
Hello Time
The length of time between broadcasts of the
hello message by the switch
2 seconds
Maximum Age
Timer
Measures the age of a received BPDU for a
port and ensures that the BPDU is discarded
when its age exceeds the value of the
maximum age timer.
20 seconds
Forward Delay
Timer
The amount time spent by a port in the
learning and listening states waiting for a
BPDU that may return the port to the blocking
state.
15 seconds
Port Level STP
The user may configure the VLAN or port STP parameters listed here:
Variable Description Default Value
Port Priority
A relative priority for each port
–
lower numbers
give a higher priority and a greater chance of a
given port being elected as the root port
32768
Port Cost
A value used by STP to evaluate paths
–
STP
calculates path costs and selects the path with the
minimum cost as the active path. 10
Bridge Protocol Data Units
The Switch uses the following information for STP to stabilize network topology:
-
The unique switch identifier
-
The path cost to the root associated with each switch port
-
The port identifier
This STP information is shared among 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 path cost to the root from the transmitting port
-
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 receive the BPDU. BPDUs 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.