Understanding Ieee 802.1Q Encapsulation; Understanding Access Vlans - Cisco Nexus 3000 series Configuration Manual

Understanding IEEE 802.1Q Encapsulation

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Understanding IEEE 802.1Q Encapsulation, on page 46
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
and packet belong. This method allows packets that are encapsulated for several different VLANs to traverse
the same port and maintain traffic separation between the VLANs.
Figure 5: Header without and with 802.1Q Tag Included

Understanding Access VLANs

When you configure a port in access mode, you can specify which VLAN will carry the traffic for that interface.
If you do not configure the VLAN for a port in access mode, or an access port, the interface carries traffic for
the default VLAN (VLAN1).
You can change the access port membership in a VLAN by specifying the new VLAN. You must create the
VLAN before you can assign it as an access VLAN for an access port. If you change the access VLAN on an
access port to a VLAN that is not yet created, the system will shut that access port down.
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.
Cisco Nexus 3000 Series NX-OS Layer 2 Switching Configuration Guide, Release 5.0(3)U1(1)
46
Configuring Access and Trunk Interfaces