interface Vlan1
 ip address 192.168.0.16 255.255.255.0 secondary
 ip address 192.168.0.1 255.255.255.0

gw#show ip arp
Protocol  Address          Age (min)  Hardware Addr   Type   Interface
Internet  192.168.0.1             -   649e.f382.e6e1  ARPA   Vlan1
Internet  192.168.0.16            -   649e.f382.e6e1  ARPA   Vlan1
...