Operation Manual – Voice VLAN
H3C S3100 Series Ethernet Switches Chapter 1 Voice VLAN Configuration
1-3
 Note:
In cases where an IP phone obtains an IP address from a DHCP server that does not
support Option 184, the IP phone directly communicates through the gateway after it
obtains an IP address. It does not go through the steps described below.
z If DHCP Server 1 supports Option 184, it returns the IP address assigned to the IP
phone, the IP address of the NCP, the voice VLAN ID, and so on.
2) On acquiring the voice VLAN ID and NCP address from DHCP Server 1, the IP
phone communicates with the specified NCP to download software, ignores the IP
address assigned by DHCP Server 1, and sends a new DHCP request message
carrying the voice VLAN tag to the voice VLAN.
3) After receiving the DHCP request, DHCP Server 2 residing in the voice VLAN
assigns a new IP address to the IP phone and sends a tagged response message
to the IP phone. After the IP phone receives the tagged response message, it
sends voice data packets tagged with the voice VLAN tag to communicate with the
voice gateway. In this case, the port connecting to the IP phone must be
configured to allow the packets tagged with the voice VLAN tag to pass.
 Note:
z An untagged packet carries no VLAN tag.
z A tagged packet carries the tag of a VLAN.
To set an IP address and a voice VLAN for an IP phone manually, just make sure that
the voice VLAN ID to be set is consistent with that of the switch and the NCP is
reachable to the IP address to be set.
1.1.2 How S3100 Series Switches Identify Voice Traffic
S3100 series Ethernet switches determine whether a received packet is a voice packet
by checking its source MAC address against an organizationally unique identifier (OUI)
list. If a match is found, the packet is considered as a voice packet. Ports receiving
packets of this type will be added to the voice VLAN automatically for transmitting voice
data.
You can configure OUI addresses for voice packets or specify to use the default OUI
addresses.
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