Understanding Ieee 802.1Q Encapsulation - Cisco nexus 5000 series Configuration Manual

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.
Only an end station can be set as a host port; you will receive an error message if you attempt to configure
Note
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.
An Ethernet interface can function as either an access port or a trunk port; it cannot function as both port
Note
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 5000 Series NX-OS Layer 2 Switching Configuration Guide, Release 5.1(3)N1(1)
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Configuring Access and Trunk Interfaces
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