Cisco Systems N3KC3048TP1GE, N3KC3064TFAL3 manual Understanding Ieee 802.1Q Encapsulation

Configuring Access and Trunk Interfaces

Understanding IEEE 802.1Q Encapsulation

The following figure shows how you can use trunk ports in the network. The trunk port carries traffic for two or more VLANs.

Figure 5: Devices in a Trunking Environment

In order to correctly deliver the traffic on a trunk port with several VLANs, the device uses the IEEE 802.1Q encapsulation or tagging method.

To optimize the performance on access ports, you can configure the port as a host port. Once the port is configured as a host port, it is automatically set as an access port, and channel grouping is disabled. Use the host designation to decrease the time it takes the designated port to begin to forward packets.

Note Only an end station can be set as a host port; you will receive an error message if you attempt to configure other ports as hosts.

If an access port receives a packet with an 802.1Q tag in the header other than the access VLAN value, that port drops the packet without learning its MAC source address.

Note An Ethernet interface can function as either an access port or a trunk port; it cannot function as both port types simultaneously.

Understanding IEEE 802.1Q Encapsulation

A trunk is a point-to-point link between the device and another networking device. Trunks carry the traffic of multiple VLANs over a single link and allow you to extend VLANs across an entire network.

To correctly deliver the traffic on a trunk port with several VLANs, the device uses the IEEE 802.1Q encapsulation (tagging) method. This tag carries information about the specific VLAN to which the frame

	Cisco Nexus 3000 NX-OS Layer 2 Switching Configuration Guide, Release 5.0(3)U3(1)
50	OL-26590-01