Allied Telesis AT-9400, User Manual

Page: 442 / 668

Chapter 23: Multiple Spanning Tree Protocol
442 Section V: Spanning Tree Protocols
3. Configure the following parameters as necessary.
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.
Note
Selecting the STP-compatible mode deletes all spanning tree
instances on the switch.
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.
When you select a value for maximum age, observer the following
rules:
MaxAge must be greater than (2 x (Hel 1)).
MaxAge must be less than (2 x (ForwardingDelay - 1))
5 - Max Hops
MSTP regions use this parameter to discard BPDUs. The Max Hop
counter in a BPDU is decremented every time the BPDU crosses a