Alcatel-Lucent OmniSwitch 6800 Series - Configuring Port Path Cost

Configuring STP Port Parameters Configuring Spanning Tree Parameters
page 7-32 OmniSwitch 6800/6850/9000 Network Configuration Guide March 2008
To change the port priority for a link aggregate, use the bridge slot/port priority commands described
above, but specify a link aggregate control number instead of a slot and port. For example, the following
command sets the priority for link aggregate 10 associated with VLAN 755 to 9:
-> bridge 755 10 priority 9
For more information about configuring an aggregate of ports, see Chapter 16, “Configuring Static Link
Aggregation,” and Chapter 17, “Configuring Dynamic Link Aggregation.”
Configuring Port Path Cost
The path cost value specifies the contribution of a port to the path cost towards the root bridge that
includes the port. The root path cost is the sum of all path costs along this same path and is the value
advertised in Configuration BPDU transmitted from active Spanning Tree ports. The lower the cost value,
the closer the switch is to the root.
Note that type of path cost value used depends on which path cost mode is active (automatic or 32-bit). If
the path cost mode is set to automatic, a 16-bit value is used when STP or RSTP is the active protocol and
a 32-bit value is used when MSTP is the active protocol. If the mode is set to 32-bit, then a 32-bit path cost
value is used regardless of which protocol is active. See “Configuring the Path Cost Mode” on page 7-25
for more information.
If a 32-bit path cost value is in use and the path_cost is set to zero, the following IEEE 802.1Q 2005
recommended default path cost values based on link speed are used:
Is a 16-bit path cost value is in use and the path_cost is set to zero, the following IEEE 802.1D recom-
mended default path cost values based on link speed are used:
By default, Spanning Tree is enabled on a port and the path cost is set to zero. If the switch is running in
the 1x1 Spanning Tree mode, then the port path cost applies to the specified VLAN instance associated
with the port. If the switch is running in the flat Spanning Tree mode, then the port path cost applies across
all VLANs associated with the port. The flat mode instance is specified as the port’s instance, even if the
port is associated with other VLANs.
Link Speed
IEEE 802.1D
Recommended Value
10 MB 2,000,000
100 MB 200,000
1 GB 20,000
10 Gbps 2,000
Link Speed
IEEE 802.1D
Recommended Value
4 Mbps 250
10 Mbps 100
16 Mbps 62
100 Mbps 19
1 Gbps 4
10 Gbps 2