Avaya 1110 Fundamentals page 389

and Auto VLAN are implemented as separate functions in the IP Phone firmware. However, in
practice, Full DHCP and Auto VLAN are frequently used together.
Full DCHP
DHCP support in the IP Phone requires sending a "Class Identifier" option with the value
"Nortel-i2004-A" in each DHCP DHCPOFFER and DHCPACK message. Additionally, the
telephone checks for either a Vendor Specific option message with a specific, unique to 2004
IP Phone, encapsulated sub-type, or a Site Specific DHCP option.
In either case, a 2004 IP Phone-specific option must be returned by the 2004 IP Phone aware
DHCP server in all Offer and Acknowledgement (ACK) messages. The IP Phone uses this
option's data it to configure the information required to connect to the TPS.
The DHCP response is parsed to extract the IP Phone's IP address, subnet mask, and gateway
IP address. The vendor specific field is then parsed to extract the Server 1 (minimum) and
optionally Server 2. By default, Server 1 is always assumed to be the "primary" server after a
DHCP session.
For the IP Phone to accept Offers/Acks, the messages must contain all of the following:
• A router option (needs a default router to function)
• A subnet mask option
• A Vendor Specific option as specified below or a Site Specific option as specified
below.
- The initial DHCP implementation required only the Vendor Specific encapsulated
sub-option. In inter-op testing with Windows NT (up to Service Release 4), it was
discovered that Windows NT does not properly adhere to RFC 1541. As a result this
option is not possible. The implementation was changed to add support for either
Vendor Specific sub-ops or Site Specific options. This new extension has been
tested and verified to work with Windows NT.
- The site-specific options are all DHCP options between 128 (0x80) and 254 (0xFE).
These options are reserved for site specific use by the DHCP RFCs.
Format for IP Phone DHCP Class Identifier Field
All IP Phones fill in the Class ID field of the DHCP Discovery and Request messages with the
following:
"Nortel-i2004-A", where:
• ASCII encoded, NULL (0x00) terminated
• unique to 2004 IP Phone
• "-A" uniquely identifies this version
Format for IP Phone DHCP Encapsulated Vendor Specific Field
This sub-option must be encapsulated in a DHCP Vendor Specific Option (refer to RFC 1541
and RFC 1533) and returned by the DHCP server as part of each DHCP OFFER and ACK
message in order for the IP Phone to accept these messages as valid.
The IP Phone parses this option's data and uses it to configure the information required to
connect to the TPS. The sub-option must be present, or a similarly encoded site-specific option
IP Deskphones Fundamentals
Network features
February 2013 389