Clone a MAC address on Cisco ASA 5505

Hi,

I’ve been trying to clone the MAC address of the
Vlan 2 interface of the Cisco ASA 5505 to match the MAC address of the existing Nortel, so that i get the same ip address from the ISP DHCP server.

All i did was
#Interface vlan 2
#mac address [Mac Address]

when i do the show interface command for Vlan 2
i do see the new MAC but when i plugged in the
cisco after doing the DHCP release on the Nortel
and power off both the Nortel and the cable modem.I am getting a diffrent IP even though our ISP has reserved that IP to MAC.

Am i cloning the MAC right on ASA ?
Please advice.