Specifications

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Cisco MWR 2941 Mobile Wireless Edge Router Release 3.5 Software Configuration Guide, Cisco IOS Release 15.1(3)MR
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Chapter 7 Configuring VLANs
Configuring VLAN Trunks
Beginning in privileged EXEC mode, follow these steps to configure the native VLAN on an
IEEE 802.1Q trunk:
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 router 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 Chapter 9, “Configuring STP.”
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 7-2 shows two trunks connecting supported switches. In this example, the switches are configured
as follows:
• 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.
Command Purpose
Step 1
configure terminal Enter global configuration mode.
Step 2
interface interface-id Define the interface that is configured as the IEEE 802.1Q trunk, and
enter interface configuration mode.
Step 3
no shutdown Enable the port, if necessary. By default, UNIs and ENIs are disabled
and NNIs are enabled.
Step 4
switchport trunk native vlan vlan-id Configure the VLAN that is sending and receiving untagged traffic
on the trunk port.
For vlan-id, the range is 1 to 4094.
Step 5
end Return to privileged EXEC mode.
Step 6
show interfaces interface-id switchport Verify your entries in the Trunking Native Mode VLAN field.
Step 7
copy running-config startup-config (Optional) Save your entries in the configuration file.