how many IP address can be assigned to one interface on the router?

hi, there is only one IP address can be assign to the interface. For example you can check the mac-address of the interface using the command "display interface g0/0/1". Different interface will have different mac-address at the end of it

I saw a concept named secondary IP address before, it says that secondary IP address can be assigned to the interface, so I'm curious how many or the maximum number of the IP address that can be assigned to the interface.

and I tried in ensp, both IP, ip address and secondary ip address, can be ping by the device

what's your product type?
I tried on the router AR3260, I can configure as most as 31 subordinate address and a main IP address, so you can configure as most as 32 IP address to an interface

@sim_157 hope this could help you,