Had an Avaya IP phone connected to Cisco ASA and not receiving an IP address from DHCP scope configured on ASA. PC connected behind the phone worked just fine. Turned out to be capitalization of DHCP options.
What I had was this:
dhcpd option 242 ascii MCIPADD=10.10.10.10,MCPORT=1719
When I changed to lower case the phone got IP address and registered.
dhcpd option 242 ascii mcipadd=10.10.10.10,mcport=1719