52
Port link
type
Configuration requirements
The port must forward packets from the voice VLAN.
Hybrid
The voice VLAN must be the PVID of the port.
The port must forward packets from the voice VLAN without VLAN tags.
Security mode and normal mode of voice VLANs
Depending on the filtering mechanisms to incoming packets, 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.
In this mode, voice VLANs are vulnerable to traffic attacks. Malicious users might send a large
number of forged voice-VLAN-tagged or untagged packets to affect voice communication.
•
Security
mode
—The port uses the source MAC addresses of voice packets to match the OUI
addresses of the device. Packets that fail the match will be dropped.
In a safe network, you can configure the voice VLANs to operate in normal mode. This mode reduces
system resource consumption in source MAC address checking.
In either mode, the device modifies the transmission priority only for voice VLAN packets whose
source MAC addresses match OUI addresses of the device.
As a best practice, do not transmit both voice traffic and non-voice traffic in a voice VLAN. If you must
transmit different traffic in a voice VLAN, make sure the voice VLAN security mode is disabled.
Table 3 Packet processing on a voice VLAN-enabled port in normal or security mode
Voice VLAN
mode
Packet type
Packet processing
Normal
•
Untagged
packets
•
Packets
with
the
voice VLAN tags
The port does not examine their source MAC addresses.
Both voice traffic and non-voice traffic can be transmitted in
the voice VLAN.
Packets with other VLAN
tags
The port forwards or drops them depending on whether the
port permits packets from these VLANs to pass through.
Security
•
Untagged
packets
•
Packets
with
the
voice VLAN tags
•
If the source MAC address of a packet matches an OUI
address on the device, the packet is forwarded in the
voice VLAN.
•
If the source MAC address of a packet does not match
an OUI address on the device, the packet is dropped.
Packets with other VLAN
tags
The port forwards or drops them depending on whether the
port permits packets from these VLANs to pass through.
Restrictions and guidelines: Voice VLAN
configuration
The aging timer of a voice VLAN starts only when the dynamic MAC address entry of the voice VLAN
ages out. The aging period for the voice VLAN equals the sum of the voice VLAN aging timer and the
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