Aastra 9143i Series Administrator's Manual page 199

Using Options 159 and 160 on the IP Phone
In addition to DHCP options 43 and 66 already supported on the IP Phones, the
phones also support DHCP Options 159 and 160. The IP Phones use the following
order of precedence when deriving the configuration server parameters: 43, 160,
159, 66.
In addition, an administrator can override this order of precedence by setting a
configuration parameter called, dhcp config option override (configuration
files), DHCP Download Options (Aastra Web UI), or Download Options (IP
Phone UI). Setting this parameter results in the phone only using the chosen
DHCP option and ignoring the other options.
For more information about setting DHCP download preference, see
"Configuration Server Download Precedence"
Configuring DHCP Download Options on the IP Phones
Use the following procedures to configure DHCP Option Override on the IP
Phone.
Configuration Files
For specific parameters you can set in the configuration files, see Appendix A, the section,
Settings" on page A-13.
41-001160-03, Rev 00, Releaes 2.4
Configuring Network and Session Initiation Protocol (SIP) Features
Warning: Administrators should review the updated IP phone DHCP
option precedence order and configuration options to avoid potential
impact to existing Aastra IP phone deployments.
Network Settings
on page 4-20..
"DHCP Option
4-17