Configuring Trunk Ports For Load Sharing; Load Sharing Using Stp Port Priorities - Cisco 3845 - Security Bundle Router Software Manual

Configuring VLAN Trunks
Command
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 sending 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 that connect 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 the VLAN to which the traffic belongs.
You configure load sharing on trunk ports that have STP enabled 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 STP 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 10-2
configured 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.
Cisco ME 3800X and 3600X Switch Software Configuration Guide
10-14
shows two trunks connecting supported switches. In this example, the switches are
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
Return to privileged EXEC mode.
Verify your entries in the Trunking Native Mode VLAN field.
(Optional) Save your entries in the configuration file.
Chapter 10 Configuring VLANs
Chapter 13, "Configuring STP."
OL-23400-01