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DBC 422
AND
DBC 425
53
1531-DBC 422 02 Uen B3 2013-12-02
7.20.1 Automatic
VLAN
detection with DHCP
Prerequisites on the LAN
When the phone is connected to a layer 2 switch, the switch will add the
IEEEE 802.1Q header, to untagged frames with the default VLAN iden-
tity and forward the frames. The first layer 3 switch must be initiated for
DHCP relay and having an ingress port with an IP address on each of
the offered VLANs. The address to the DHCP server must be set in the
layer 3 switch.
When the layer 3 switch has received a
DHCP discover
message, it will
forward this packet to the DHCP server adding the IP address of its
ingress port corresponding to the VLAN. It is this address information
that informs the DHCP server to which IP subnet that this phone is to be
assigned to.
Description of when a
VLAN identity list is received from the native
LAN
At installation (and hardware reboot) the phone asks for a temporary IP
address from DHCP by initiating the DHCP negotiation with untagged
messages (native LAN). The relay agent adds the address of its ingress
port corresponding to the native LAN. DHCP provides the temporary IP
address together with the VLAN identity list. The phone releases the
temporary IP address.
Then the phone uses the first VLAN identity in the list and sends a new
tagged request to the DHCP server. The relay agent adds the address
of the ingress port corresponding to the
selected
VLAN. If there is any
available IP address, the DHCP server provides this address to the
phone. If there is no available IP address for this VLAN, the phone takes
the next VLAN id in the list and asks for an IP address.
If there is no IP address available in any VLAN in the list, the phone will
ask for an IP address in the native LAN.
Reboot
It is possible to specify in the configuration file whether the telephone
should retain the previously used VLAN identity after reboot, or whether
it should start a new automatic VLAN detection procedure. See descrip-
tion for Configuration file for DBC42x.
To change the VLAN identity:
See description for Configuration file for DBC42x.
7.20.2 Assigning
the
VLAN identity via the configuration file
The description of the parameters, see the description for
CONFIGURA-
TION FILE FOR DBC 42X
.
The configuration file is read from the native LAN