Load Sharing Using Stp Port Priorities; Configuring Stp Port Priorities And Load Sharing - Cisco Catalyst 2950 Software Manual

Chapter 8 Configuring VLANs
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 transmits or receives all traffic
for the VLAN.
Figure 8-4
as follows:
•
•
•
•
In this way, trunk 1 carries traffic for VLANs 8 through 10, and trunk 2 carries traffic for VLANs 3
through 6. If the active trunk fails, the trunk with the lower priority takes over and carries the traffic for
all of the VLANs. No duplication of traffic occurs over any trunk port.
Figure 8-4
VLANs 8 – 10 (priority 10)
VLANs 3 – 6 (priority 128)

Configuring STP Port Priorities and Load Sharing

Beginning in privileged EXEC mode, follow these steps to configure the network shown in
Command
Step 1
vlan database
Step 2 vtp domain
domain-name
Step 3
vtp server
78-11380-03
shows two trunks connecting supported switches. In this example, the switches are configured
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.
Load Sharing by Using STP Port Priorities
Trunk 1
Switch 2
Purpose
On Switch 1, enter VLAN configuration mode.
Configure a VTP administrative domain.
The domain name can be from 1 to 32 characters.
Configure Switch 1 as the VTP server.
"Understanding Basic STP Features" section on page
Switch 1
Trunk 2
VLANs 3 – 6 (priority 10)
VLANs 8 – 10 (priority 128)
Catalyst 2950 Desktop Switch Software Configuration Guide
Load Sharing Using STP
9-1.
Figure 8-4:
8-25