Question

Which device have Exactly one i/p address? (Work Station,Router,Gateway can have more than one i/p)

Comments

why do you think that router,gateway,workstation  has more than one ip address every devicehas a unique ip address

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@vishal 

IP Addresses are allocated by network administrator to each communicating device ( like router /gateway/workstations) that participate in a network.  For each network there is one IP address . Router, gateway and workstations can handle multiple networks so for each networks they have  separate IP address that leads to Multiple IP addresses .

But each device have Unique MAC address .

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very well explained

Answer 1

Exactly 1 IP address is not possible for any device, theoretically.

Each communicating device which use Internet get the internet from an ISP which provide IP address  to that device. Now when that device change that ISP and use another internet from another ISP that leads to another IP address for same communicating device. 

In a single local network (i.e. flat network or VLAN) a single IP address can only be assigned to one interface/device at any given time. 

so it is not possible for a device to have exactly one IP address .

For further reference you can read :

1. https://www.quora.com/How-does-each-computer-in-the-world-have-a-unique-IP-address
2. https://networkengineering.stackexchange.com/questions/23751/how-many-ip-addresses-can-a-device-or-an-interface-possess