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Voice VLAN assignment modes
A port can be assigned to a voice VLAN automatically or manually.
Automatic mode
When an IP phone is powered on, it sends out protocol packets. After receiving these protocol
packets, the device uses the source MAC address of the protocol packets to match its OUI
addresses. If the match succeeds, the device performs the following operations:
•
Assigns the receiving port of the protocol packets to the voice VLAN.
•
Issues ACL rules and sets the packet precedence.
•
Starts the voice VLAN aging timer.
If no voice packet is received from the port before the aging timer expires, the device will remove the
port from the voice VLAN. The aging timer is also configurable.
Manual mode
You must manually assign the port that connects to the IP phone to a voice VLAN. The device uses
the source MAC address of the received voice packets to match its OUI addresses. If the match
succeeds, the device issues ACL rules and sets the packet precedence.
Security mode and normal mode of voice VLANs
Depending on the incoming packet filtering mechanisms, a voice VLAN-enabled port can operate in
one of the following modes:
•
Normal
mode
—The port receives voice-VLAN-tagged packets and forwards them in the voice
VLAN without examining their MAC addresses. If the PVID of the port is the voice VLAN and the
port operates in manual VLAN assignment mode, the port forwards all the received untagged
packets in the voice VLAN.
•
Security
mode
—The port uses the source MAC addresses of the received packets to match
the OUI addresses of the device. Packets that fail the match will be dropped.
MAC
An Ethernet device uses a MAC address table to forward frames. A MAC address entry includes a
destination MAC address, an outgoing interface (or egress RB), and a VLAN ID. When the device
receives a frame, it uses the destination MAC address of the frame to look for a match in the MAC
address table.
•
The device forwards the frame out of the outgoing interface in the matching entry if a match is
found.
•
The device floods the frame in the VLAN of the frame if no match is found.
Types of MAC address entries
A MAC address table can contain the following types of entries:
•
Dynamic
entries
—A dynamic entry can be manually configured or dynamically learned to
forward frames with a specific destination MAC address out of the associated interface. A
dynamic entry might age out. A manually configured dynamic entry has the same priority as a
dynamically learned one.
•
Static
entries
—A static entry is manually added to forward frames with a specific destination
MAC address out of the associated interface, and it never ages out. A static entry has higher
priority than a dynamically learned one.