Configuring Vlan Bridge Max Age Time; Configuring Vlan Bridge Forward Delay Time - Alcatel OmniSwitch 6800 Series Network Configuration Manual

Configuring STP VLAN Parameters

Configuring VLAN Bridge Max Age Time

The VLAN bridge max age time specifies how long, in seconds, the bridge retains Spanning Tree informa-
tion it receives from Configuration BPDU. When a bridge receives a BPDU, it updates its configuration
information and the max age timer is reset. If the max age timer expires before the next BPDU is received,
the bridge will attempt to become the root, designated bridge, or change its root port.
The max age time propagated in a root bridge Configuration BPDU is the value used by all other bridges
in the tree for their own max age time. Therefore, if this value is changed for the root bridge (VLAN), all
other VLANs associated with the same STP instance will adopt this value as well.
If the switch is running in the 1x1 Spanning Tree mode, then a max age time value is defined for each
VLAN. When a VLAN is created, STP is enabled and the max age time defaults to 20 seconds. If the
switch is running in the flat Spanning Tree mode, then the max age value is defined for instance 0. Speci-
fying a low max age time may cause STP to reconfigure the topology more often.
To change the VLAN bridge max age time, enter bridge followed by an existing VLAN ID (or 0 if using
the flat STP instance) then max age followed by a numerical value between 6 and 40 to specify the
number of seconds. For example, the following commands change the max age time value for VLAN 455
to 40 seconds and the max age time value for the flat STP instance to 10:
-> bridge 455 max age 40
-> bridge 0 max age 10
To view the VLAN max age time value, use the
this command, see the OmniSwitch CLI Reference Guide.

Configuring VLAN Bridge Forward Delay Time

The VLAN bridge forward delay time specifies how long, in seconds, a port remains in the listening and
learning states while it is transitioning to a forwarding state. In addition, when a topology change occurs,
the forward delay time value is used to age out all dynamically learned addresses in the MAC address
forwarding table. For more information about the MAC address table, see
Learning."
The forward delay time propagated in a root bridge Configuration BPDU is the value used by all other
bridges in the tree for their own forward delay time. Therefore, if this value is changed for the root bridge
(VLAN), all other VLANs associated with the same STP instance will adopt this value as well.
If the switch is running in the 1x1 Spanning Tree mode, then a forward delay time value is defined for
each VLAN. When a VLAN is created, STP is enabled and the forward delay time defaults to 15 seconds.
If the switch is running in the flat Spanning Tree mode, then the forward delay time value is defined for
instance 0. Specifying a low forward delay time may cause temporary network loops, because packets may
get forwarded before STP configuration or change notices have reached all nodes in the network.
To change the VLAN bridge forward delay time, enter bridge followed by an existing VLAN ID (or 0 if
using the flat STP instance) then forward delay followed by a numerical value between 4 and 30 to spec-
ify the number of seconds. For example, the following commands change the forward delay time value for
VLAN 455 to 10 seconds and the forward delay time value for the flat STP instance to 15:
-> bridge 455 forward delay 10
-> bridge 0 forward delay 15
To view the VLAN forward delay time value, use the
about this command, see the OmniSwitch CLI Reference Guide.
page 5-14
show spantree
show spantree
OmniSwitch 6800 Series Network Configuration Guide
Configuring Spanning Tree Parameters
command. For more information about
Chapter 2, "Managing Source
command. For more information
November 2004