Alcatel 9000 Betriebsanweisung PDF herunterladen (Seite 132)

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Configuring STP Bridge Parameters Configuring Spanning Tree Parameters

page 6-16 OmniSwitch 6800/6850/9000 Network Configuration Guide June 2006

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.

If the switch is running in the 1x1 Spanning Tree mode, then a hello time value is defined for each VLAN

instance. If the switch is running in the flat Spanning Tree mode, then a hello time value is defined for the

single flat mode instance. In both cases, the default hello time value used is 2 seconds.

To change the bridge hello time value for a VLAN instance, specify a VLAN ID with the bridge hello

time command when the switch is running in the 1x1 mode. For example, the following command

changes the hello time for VLAN 455 to 5 seconds:

-> bridge 455 hello time 5

The explicit bridge 1x1 hello time command configures the hello time value 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 hello time 5

To change the bridge hello time value for the flat mode instance, use either the bridge hello time

command or the bridge cist hello time 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 hello time value for the flat mode instance to 12288:

-> bridge hello time 10

-> bridge cist hello time 10

As in previous releases, it is possible to configure the flat mode instance with the bridge hello time

command by specifying 1 as the instance number (e.g., bridge 1 hello time 5). However, this is only

available when the switch is already running in the flat mode and STP or RSTP is the active protocol.

Note that the bridge hello time is not configurable for 802.1s Multiple Spanning Tree Instances (MSTI).

These instances inherit the hello time from the flat mode instance (CIST).

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