3com S7906E Manuel De Montage

 

4-4 

VLANs are vulnerable to traffic attacks. Vicious users can forge a large amount of voice packets 

and send them to voice VLAN-enabled ports to consume the voice VLAN bandwidth, affecting 

normal voice communication.  

z 

Security mode: In this mode, only voice packets whose source MAC addresses comply with the 

recognizable OUI addresses can pass through the voice VLAN-enabled inbound port, while all 

other packets are dropped. 

In a safe network, you can configure the voice VLANs to operate in normal mode, thus reducing the 

consumption of system resources due to source MAC addresses checking. It is recommended not to 

transmit both voice packets and non-voice packets in a voice VLAN. If you have to, please ensure that 

the voice VLAN security mode is disabled. 

Table 4-3 How a voice VLAN-enable port processes packets in security/normal mode 

Untagged packets 

Packets carrying the 
voice VLAN tag 

If the source MAC address of a packet matches an OUI 
address configured for the device, it is forwarded in the 
voice VLAN; otherwise, it is dropped. 

Security mode 

Packets carrying 
other tags 

Forwarded or dropped depending on whether the port 
allows packets of these VLANs to pass through 

Untagged packets 

Packets carrying the 
voice VLAN tag 

The port does not check the source MAC addresses of 
inbound packets. All types of packets can be transmitted 
in the voice VLAN. 

Normal mode 

Packets carrying 
other tags 

Forwarded or dropped depending on whether the port 
allows packets of these VLANs to pass through 

 

Before configuring a VLAN as a voice VLAN, create the VLAN first. Note that you cannot configure 

VLAN 1 (the system-default VLAN) as a voice VLAN.  

Follow these steps to set a port to operate in automatic voice VLAN assignment mode: 

Enter system view 

— 

Set the voice VLAN aging time 

voice vlan aging minutes 

Optional 

1440 minutes by default.  

The voice VLAN aging time 
configuration is only applicable 
on ports in automatic voice 
VLAN assignment mode.  

Enable the voice VLAN security 
mode 

Optional 

Enabled by default.