Configuring Spanning Tree Parameters Configuring STP Bridge Parameters
OmniSwitch AOS Release 6 Network Configuration Guide September 2009 page 13-21
To change the bridge priority value for a VLAN instance, specify a VLAN ID with the bridge priority
command when the switch is running in the 1x1 mode. For example, the following command changes the
priority for VLAN 455 to 25590:
-> bridge 455 priority 25590
The explicit bridge 1x1 priority command configures the priority for a VLAN instance when the switch
is running in either mode (1x1 or flat). For example, the following command performs the same function
as the command in the previous example:
-> bridge 1x1 455 priority 25590
Note. If PVST+ mode is enabled on the switch, then the priority values can be assigned only in the multi-
ples of 4096 to be compatible with the Cisco MAC Reduction mode; any other values will result in an
error message.
To change the bridge priority value for the flat mode instance, use either the bridge priority command or
the bridge cist priority command. Note that both commands are available when the switch is running in
either mode (1x1 or flat) and an instance number is not required. For example, the following commands
change the priority value for the flat mode instance to 12288:
-> bridge priority 12288
-> bridge cist priority 12288
As in previous releases, it is possible to configure the flat mode instance with the bridge protocol
command by specifying 1 as the instance number (e.g., bridge 1 protocol rstp). However, this is only
available when the switch is already running in the flat mode and STP or RSTP is the active protocol.
The bridge priority value is also configurable for a Multiple Spanning Tree Instance (MSTI). To config-
ure this value for an MSTI, use the explicit bridge msti priority command and specify the MSTI ID for
the instance number and a priority value that is a multiple of 4096. For example, the following command
configures the priority value for MSTI 10 to 61440:
-> bridge msti 10 priority 61440
Note that when MSTP is the active flat mode protocol, explicit Spanning Tree bridge commands are
required to configure parameter values. Implicit commands are for configuring parameters when the STP
or RSTP protocols are in use. See Chapter 12, “Using 802.1Q 2005 Multiple Spanning Tree,” for more
information.
Configuring the Bridge Hello Time
The bridge hello time interval is the number of seconds a bridge will wait between transmissions of
Configuration BPDU. When a bridge is attempting to become the root or if it has become the root or a
designated bridge, it sends Configuration BPDU out all forwarding ports once every hello time value.
The hello time propagated in a root bridge Configuration BPDU is the value used by all other bridges in
the tree for their own hello time. Therefore, if this value is changed for the root bridge, all other bridges
associated with the same STP instance will adopt this value as well.
Note that lowering the hello time interval improves the robustness of the Spanning Tree algorithm.
Increasing the hello time interval lowers the overhead of Spanning Tree processing.
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