Configuring Spanning Tree Parameters Configuring STP Bridge Parameters
OmniSwitch AOS Release 8 Network Configuration Guide December 2017 page 6-30
To change the max-age time value for the flat mode CIST instance, use either the spantree max-age
command or the spantree max-age command with the cist parameter. Note that both commands are
available when the switch is running in either mode (per-VLAN or flat). For example, the following
commands change the max-age time value for the flat mode instance to 10:
-> spantree max-age 10
-> spantree cist max-age 10
Configuring the Forward Delay Time for the Switch
The bridge forward delay time specifies how long, in seconds, a port remains in the learning state 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 Chapter 3, “Managing Source 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,
all other bridges associated with the same instance adopt this value as well.
If the switch is running in the per-VLAN Spanning Tree mode, then a forward delay time value is defined
for each VLAN instance. If the switch is running in the flat Spanning Tree mode, then the forward delay
time value is defined for the flat mode instance. In both cases, the default forward delay time is used.
To change the bridge forward delay time value for a VLAN instance regardless of which mode (per-
VLAN or flat) is active for the switch, use the spantree forward-delay command with the vlan
parameter. For example, the following command changes the forward delay time for VLAN 455 to 10
seconds:
-> spantree vlan 455 forward-delay 10
To change the forward-delay time value for the flat mode CIST instance, use either the spantree forward-
delay command or the spantree forward-delay command with the cist parameter. Note that both
commands are available when the switch is running in either mode (per-VLAN or flat). For example, the
following commands change the forward-delay time value for the flat mode instance to 10:
-> spantree forward-delay 10
-> spantree cist forward-delay 10
Enabling/Disabling the VLAN BPDU Switching Status
BPDU are not switched on ports associated with VLANs that have Spanning Tree disabled. This can result
in a network loop if the VLAN has redundant paths to one or more other switches. Allowing VLANs that
have Spanning Tree disabled to forward BPDU to all ports in the VLAN, can help to avoid this problem.
Note. The max-age time is not configurable for Multiple Spanning Tree Instances (MSTI). These instances
inherit the max-age time from the flat mode instance (CIST).
Note. Specifying a low forward delay time can cause temporary network loops, because packets can get
forwarded before Spanning Tree configuration or change notices have reached all nodes in the network.
Note. The forward delay time is not configurable for Multiple Spanning Tree Instances (MSTI). These
instances inherit the forward delay time from the flat mode instance (CIST).
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