Configuring Basic Features
December 2000 10 - 35
or on the Layer 2 or Layer 3 Switch (when no VLANs are configured for the system). Ports are re-routed
based on their priority. A higher numerical value means a lower priority; thus, the highest priority is 0.
Possible values: 0 – 255. Default is 128.
• Path Cost – This parameter can be used to assign a higher or lower path cost to a port. This value can be
used to bias traffic toward or away from a certain path during periods of rerouting. For example, if you wish to
bias traffic away from a certain port, assign it a higher value than other ports within the VLAN or all other ports
(when VLANs are not active on the Layer 2 or Layer 3 Switch). Possible values are 0 – 65535. The default
values are listed in Table 10.4.
Notice that the path costs favor 100 Mbps and faster Ethernet ports over Packet over SONET (POS) ports. STP
applies to POS ports only when they are configured for remote bridging to support Point-to-Point Protocol (PPP).
(See “Configuring POS for Layer 2 Switching” on page 6-11.) The POS paths are remote (WAN) paths and the
Ethernet paths are local paths. The default path costs therefore favor local paths over remote paths.
USING THE CLI
EXAMPLE:
Suppose you want to enable STP on a system in which no port-based VLANs are active and change the hello-
time from the default value of 2 to 8 seconds. Additionally, suppose you want to change the path and priority costs
for port 5 only. To do so, enter the following commands.
BigIron(config)# span hello-time 8
BigIron(config)# span ethernet 5 path-cost 15 priority 64
Here is the syntax for global STP parameters.
Syntax: span [forward-delay <value>] | [hello-time <value>] | [maximum-age <time>] | [priority <value>]
Here is the syntax for STP port parameters.
Syntax: span ethernet <portnum> path-cost <value> | priority <value>
USING THE WEB MANAGEMENT INTERFACE
To modify the STP parameters:
1. Log on to the device using a valid user name and password for read-write access. The System configuration
panel is displayed.
2. Click on the plus sign next to Configure in the tree view to display the configuration options.
3. Select the STP
link to display the STP bridge and port parameters.
4. Click the Modify button in the STP bridge row to display the STP configuration panel, as shown in the
following example.
Table 10.4: Default STP Port Path Costs
Port Type Default Path Cost
10 Mbps 100
100 Mbps 19
Gigabit 4
OC-3c 200
OC-12c 80
OC-48c 20
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