Allied Telesis AT-S62 - Manual (Page 524)

Chapter 23: Multiple Spanning Tree Protocol
524 Section IV: Spanning Tree Protocols
The hello time, forwarding delay, and max age parameters will have
two values if MSTP is enabled on the switch (for example, Forwarding
Delay .. 15/15). The first number is the configured value on the switch
for the parameter and the second is the value the switch obtained from
the root bridge and is actually using for the parameter. The switch
displays only the configured values for these parameters if multiple
spanning tree is not enabled on the switch.
3. Adjust the MSTP settings as needed. Changes are immediately
activated on the switch. The selections are described below.
1 - Force Version
This selection determines whether the bridge operates with MSTP or
in an STP-compatible mode. If you select MSTP, the bridge operates
all ports in MSTP, except for those ports that receive STP or RSTP
BPDU packets. If you select Force STP Compatible, the bridge uses
its MSTP parameter settings, but sends only STP BPDU packets from
the ports.
2 - Hello Time
The time interval between generating and sending configuration
messages by the bridge. The range of this parameter is 1 to 10
seconds. The default is 2 seconds. This value is active only if the
bridge is selected as the root bridge of the network.
3 - Forwarding Delay
The waiting period before a bridge changes to a new state, for
example, becomes the new root bridge after the topology changes. If
the bridge transitions too soon, not all links may have yet adapted to
the change, possibly resulting in a network loop. The range is 4 to 30
seconds. The default is 15 seconds. This setting applies only to ports
running in the STP-compatible mode.
4 - Max Age
The length of time after which stored bridge protocol data units
(BPDUs) are deleted by the bridge. This parameter applies only if the
bridged network contains an STP or RSTP single-instance spanning
tree. Otherwise, the bridges use the Max Hop counter to delete
BPDUs.
All bridges in a single-instance bridged LAN use this aging time to test
the age of stored configuration messages called bridge protocol data
units (BPDUs). For example, if you use the default of 20, all bridges
delete current configuration messages after 20 seconds. The range of
this parameter is 6 to 40 seconds. The default is 20 seconds.
In selecting a value for maximum age, the following must be observed:
MaxAge must be greater than (2 x (HelloTime + 1))
MaxAge must be less than (2 x (ForwardingDelay - 1))