Understanding Access Vlans - Cisco AP775A - Nexus Converged Network Switch 5010 Configuration Manual

Information About Access and Trunk Interfaces
To correctly deliver the traffic on a trunk port with several VLANs, the device uses the IEEE 802.1Q
encapsulation (tagging) method that uses a tag that is inserted into the frame header. 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. The encapsulated VLAN tag also allows the trunk to move traffic end-to-end through the network
on the same VLAN.
Figure 12: 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.
Note If you assign an access VLAN that is also a primary VLAN for a private VLAN, all access ports with that
access VLAN will also receive all the broadcast traffic for the primary VLAN in the private VLAN mode.
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Cisco Nexus 5000 Series Switch CLI Software Configuration Guide
Understanding Access VLANs
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