Configuring Trunk Ports For Load Sharing - Cisco Catalyst 3560-X Software Configuration Manual

Configuring VLAN Trunks
Beginning in privileged EXEC mode, follow these steps to configure the native VLAN on an
IEEE 802.1Q trunk:
Command
Step 1 configure terminal
Step 2
interface interface-id
Step 3
switchport trunk native vlan vlan-id
Step 4
end
Step 5 show interfaces interface-id switchport
Step 6 copy running-config startup-config
To return to the default native VLAN, VLAN 1, use the no switchport trunk native vlan interface
configuration command.
If a packet has a VLAN ID that is the same as the outgoing port native VLAN ID, the packet is sent
untagged; otherwise, the switch sends the packet with a tag.

Configuring Trunk Ports for Load Sharing

Load sharing divides the bandwidth supplied by parallel trunks connecting switches. To avoid loops,
STP normally blocks all but one parallel link between switches. Using 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
Load Sharing Using STP Port Priorities
When two ports on the same switch form a loop, the switch uses the STP port priority to decide which
port is enabled and which port is in a blocking state. 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 1-3
as follows:
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•
•
•
Catalyst 3750-X and 3560-X Switch Software Configuration Guide
1-22
shows two trunks connecting supported switches. In this example, the switches are configured
VLANs 8 through 10 are assigned a port priority of 16 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 16 on Trunk 2.
VLANs 8 through 10 retain the default port priority of 128 on Trunk 2.
Purpose
Enter global configuration mode.
Define the interface that is configured as the IEEE 802.1Q trunk, and
enter interface configuration mode.
Configure the VLAN that is sending and receiving untagged traffic
on the trunk port.
For vlan-id, the range is 1 to 4094.
Return to privileged EXEC mode.
Verify your entries in the Trunking Native Mode VLAN field.
(Optional) Save your entries in the configuration file.
Chapter 1, "Configuring STP."
Chapter 1 Configuring VLANs
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