You might need to create or remove an alias if you are changing the IP address of an interface. Use the alias command to create an alias IP address, and use the -alias command to remove an alias IP address.
The following example gives the interface e0 (already configured with IP address 172.28.50.21) the alias IP address 172.28.50.30:
ifconfig e0 alias 172.28.50.30
The following example removes the 172.28.50.30 alias for the interface e0 specified in the previous example:
ifconfig e0 -alias 172.28.50.30