Westermo MDI-112-F4G - Manual (Page 65)

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Note: The Web GUI allows user select the priority number directly. This is the
convenience of the GUI design. When you configure the value through the CLI or
SNMP, you may need to type the value directly. Please follow the n x 4096 rules
for the Bridge Priority.
Max Age (6-40): Enter a value from 6 to 40 seconds here. This value represents the
time that a bridge will wait without receiving Spanning Tree Protocol configuration
messages before attempting to reconfigure.
If the managed Switch is not the root bridge, and if it has not received a hello
message from the root bridge in an amount of time equal to Max Age, then the
Managed Switch will reconfigure itself as a root bridge. Once two or more devices
on the network are recognized as a root bridge, the devices will renegotiate to set
up a new spanning tree topology.
The MAX Age value affects the maximum volume of the RSTP loop. In the RSTP
BPDU packet, there is one field, message age which start from 0, add 1 after
passed one hop in the RSTP loop. When the message age is larger than MAX Age,
the BPDU would be ignored and the lower switches are separated to different
RSTP domain. The switches in other RSTP domain can’t be managed through upper
switch.
Since different RSTP aware switches may have their own mechanism to calculate
the message age. So that this is most possibly occurred when interoperate
different vendors’ RSTP aware switches together. The maximum volume of the
RSTP domain is 23, configure the MAX Age lower than 23 is recommended.
Hello Time (1-10): Enter a value from 1 to 10 seconds here. This is a periodic timer
that drives the switch to send out BPDU (Bridge Protocol Data Unit) packet to
check current STP status.
The root bridge of the spanning tree topology periodically sends out a “hello”
message to other devices on the network to check if the topology is “healthy”. The
“hello time” is the amount of time the root has waited during sending hello
messages.
Forward Delay Time (4-30): Enter a value between 4 and 30 seconds. This value is
the time that a port waits before changing from Spanning Tree Protocol learning
and listening states to forwarding state.
This is the amount of time of the Managed Switch will wait before checking to see
if it should be changed to a different state.
Once you have completed your configuration, click on Apply to apply your
settings.
Note: You must observe the following rule to configure Hello Time, Forwarding
Delay, and Max Age parameter
× (Forward Delay Time – 1 sec) ≥ Max Age Time ≥ 2 × (Hello Time value + 1 sec)
4.4.2 STP Port Configuration
This page allows you to configure the port parameter after enabled STP or RSTP.