Specifications

Engineering Guidelines
242
Unused options MUST be left blank. Conflict may arise where a number of different devices
exist within the same subnet or DHCP scope (e.g. it is known that Microsoft Server 2003 also
uses options 132 and 133). It may be necessary to redefine options, or place some equipment
in different scopes, or select options based on device MAC address. Otherwise phones will
read this information and may give unpredictable results.
IP Phone behavior
The IP Phone is very forgiving of information received through DHCP. It will allow for any of the
three possible methods mentioned for delivery of the configuration, and within the
vendor-specific methods will account for variability found in how 3rd Party DHCP servers deliver
option 43 or option 125 formats (see “Support of solution by external DHCP servers” on
page 244.)
The following behavior rules apply to the IP Phone for received DHCP parameters:
• IP Phone will accept any one of the three methods; option 125, option 43, or options
128-135, in order of priority.
- If more than one method is received in the same DHCP offer, the one with highest
priority will be applied.
• Within option 43 or option 125 responses, the IP Phone will accept the following formats
from the DHCP server side:
- Option 43 or 125, with no sub-options,
- Option 43 or 125, containing a single sub-option, ID = 1
- Within the sub-option method, the final sub-option may be ID 0xFF, the “end of
options” option (as per RFC 2132).
- Within any of above, you may have to null-terminate with 0x00 character.
132 long word 802.1Q Layer 2 VLAN ID
133 long word 802.1Q/D Layer 2 Priority
134 long word Diffserv Code Point (DSCP)
135 string HTTP Proxy for phone-specific applications
Note: The “Encapsulated vendor-specific options” formatting as defined in RFC 2132
and RFC 3925 is not normally used in the Mitel-specific exchange, however it is
accommodated by the IP Phone in order to support 3rd party DHCP severs that require it.
Table 73: Mitel-Internal current DHCP Option Usage (continued)
DHCP option Field Type Description