Configuring The Path Cost Mode; Using Automatic Vlan Containment - Alcatel-Lucent OmniSwitch 9900 Series Network Configuration Manual

Configuring Spanning Tree Parameters
To enable or disable the switching of Spanning Tree BPDU for all VLAN and CIST instances when the
switch is running in the per-VLAN mode, use the
-> spantree bpdu-switching enable
-> spantree bpdu-switching disable
To enable or disable the switching of Spanning Tree BPDU for only the CIST instance when the switch is
running in the flat mode, use the
-> spantree cist bpdu-switching enable
-> spantree cist bpdu-switching disable
To enable or disable BPDU switching on a VLAN, use the vlan parameter along with spantree bpdu-
switching command
disable it on VLAN 20:
-> spantree vlan 10 bpdu-switching enable
-> spantree vlan 20 bpdu-switching disable
Note. Disabling BPDU switching on a Spanning Tree disabled VLAN must not cause network loops to go
undetected.

Configuring the Path Cost Mode

The path cost mode controls whether the switch uses a 16-bit port path cost (PPC) or a 32-bit PPC. When
a 32-bit PPC switch connects to a 16-bit PPC switch, the 32-bit switch has a higher PPC value that
advertises an inferior path cost to the 16-bit switch. In this case, it is desirable to set the 32-bit switch to
use STP or RSTP with a 16-bit PPC value.
The path cost mode is automatically set to use a 16-bit value for all ports that are associated with an STP
instance or an RSTP instance and a 32-bit value for all ports associated with an MSTP value. It is also
possible to set the path cost mode to always use a 32-bit regardless of which protocol is active.
To change the path cost mode, use the
PPC value based on protocol) or 32bit (always use a 32-bit PPC value). For example, the following
command changes the default path cost mode from auto to 32-bit:
-> spantree path-cost-mode 32bit
Note. Cisco supports two default path cost modes: long or short just like in OmniSwitch per-VLAN
implementation. If you have configured PVST+ mode in the OmniSwitch, it is recommended that the same
default path cost mode must be configured in the same way in all the switches, so that, the path costs for
similar interface types are consistent when connecting ports between OmniSwitch and Cisco switches.

Using Automatic VLAN Containment

In a Multiple Spanning Tree (MST) configuration, it is possible for a port that belongs to a VLAN that is
not a member of an instance to become the root port for that instance. This can cause a topology change
that could lead to a loss of connectivity between VLANs/switches. Enabling Automatic VLAN
Containment (AVC) helps to prevent this from happening by making such a port an undesirable choice for
the root.
OmniSwitch AOS Release 8 Network Configuration Guide
spantree bpdu-switching
For example, the following commands enable BPDU switching on VLAN 10 and
.
spantree path-cost-mode
Configuring STP Bridge Parameters
spantree bpdu-switching
command:
command and specify either auto (uses
December 2017
command:
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