Avaya 1110 Fundamentals page 392

Features
Either this site specific option must be present or a similarly encoded vendor-specific option
must be sent (as previously described). For example, configure the DHCP server to send one
or the other – not both.
The choice of using either Vendor Specific or Site Specific options is provided to enable
Windows NT DHCP servers to be used with the IP Phone. Windows NT servers do not properly
implement the Vendor Specific Option and as a result, Windows NT implementations must use
the Site Specific version.
Format of the DHCP Site Specific field
The format of the DHCP Site Specific field is the same as the format of the Encapsulated
Vendor Specific Sub-option field. See
field on page 390.
DHCP Auto Discovery
DHCP Auto Discovery must be used only if the telephone and PC are:
• connected to the same Layer 2 switch port through a three-port switch
• on separate sub-nets
The DHCP server can be configured to supply the VLAN information to the IP Phones. The
server uses the Site Specific option in the DHCP offer message to convey the VLAN information
to the IP Phone.
Configuring a DHCP Server for VLAN Discovery is optional. This configuration is done in
addition to any done for Full DHCP configuration and it is required only when configuring the
VLAN Auto Discovery.
802.1Q VLAN support is configured using the display interface of the IP Phones during the
initial configuration procedure of the IP Phone.
This method is based on the assumption that the default VLAN will be the data VLAN and the
tagged VLAN will be the voice VLAN. Enter the voice VLAN information into the data VLAN
and subnet's DHCP server. Enter the standard IP Phone configuration string into the voice
VLAN and subnet's DHCP server pool.
The following definition describes the 2004 IP Phone-specific, Site Specific option. This option
uses the "reserved for Site Specific use" DHCP options (DHCP option values 128 to 254) and
must be returned by the DHCP server as part of each DHCPOFFER and DHCPACK message
for the IP Phone to accept these messages as valid. The IP Phone extracts the relevant
information and uses the information to configure itself.
Format of the field
The format of the field is: Type, Length, Data.
Type (1 octet):
There are five choices:
• 0x80 (128)
• 0x90 (144)
392 IP Deskphones Fundamentals
Format of the Encapsulated Vendor Specific Sub-option
Comments? infodev@avaya.com
February 2013