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Load Sharing Using STP
Configuring the CoS Port Priorities
Beginning in privileged EXEC mode, follow these steps to set the port priority for untagged (native)
Ethernet frames:
Command
Step 1
configure terminal
Step 2
interface interface
Step 3
switchport priority default
default-priority-id
Step 4
end
Step 5
show interface interface-id
switchport
Load Sharing Using STP
Load sharing divides the bandwidth supplied by parallel trunks connecting switches. To avoid loops,
STP normally blocks all but one parallel link between switches. With load sharing, you divide the traffic
between the links according to which VLAN the traffic belongs.
You configure load sharing on trunk ports by using STP port priorities or STP path costs. For load
sharing using STP port priorities, both load-sharing links must be connected to the same switch. For load
sharing using STP path costs, each load-sharing link can be connected to the same switch or to two
different switches.
For more information about STP, see the
Load Sharing Using STP Port Priorities
When two ports on the same switch form a loop, the STP port priority setting determines which port is
enabled and which port is in standby mode. You can set the priorities on a parallel trunk port so that the
port carries all the traffic for a given VLAN. The trunk port with the higher priority (lower values) for
a VLAN is forwarding traffic for that VLAN. The trunk port with the lower priority (higher values) for
the same VLAN remains in a blocking state for that VLAN. One trunk port sends or receives all traffic
for the VLAN.
Figure 8-5
configured as follows:
•
•
•
•
Catalyst 2900 Series XL and Catalyst 3500 Series XL Software Configuration Guide
8-32
Purpose
Enter global configuration mode.
Enter the interface to be configured.
Set the port priority on the interface.
If you assign a priority level from 0 to 3, frames are forwarded to the normal
priority queue of the output port.
If you assign a priority level from 4 to 7, frames are forwarded to the
high-priority queue of the output port.
Return to privileged EXEC mode.
Verify your entries. In the display, check the Priority for Untagged Frames
field.
shows two trunks connecting supported switches. In this example, the switches are
VLANs 8 through 10 are assigned a port priority of 10 on trunk 1.
VLANs 3 through 6 retain the default port priority of 128 on trunk 1.
VLANs 3 through 6 are assigned a port priority of 10 on trunk 2.
VLANs 8 through 10 retain the default port priority of 128 on trunk 2.
"Configuring STP" section on page
Chapter 8
Configuring VLANs
6-33.
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