Actually,Both IP AND MAC Address are unique in the entire world because
IP = Network ID + Subnet ID + Host ID
Subnet is determined by the Subnet Mask.
MAC = VendorID + Manufacturing Date + Serial Number
So, No two NICs in the world are same.
and theoretically MAC can be used like an IP ADDRESS but practically, it is not possible as it is not helpful in identifying the Target Network, Target Subnetwork and Host using VendorID, Manufacturing Date and Serial Number.
and theoretically IP ADDRESS can ALSO be used like MAC but practically, it is not possible as it is a software number and keeps changing after the expiry of "lease time". So, if it changes frequently then for every packet we may need to send a query request asking for the updated IP Address or it may be possible that if IP ADDRESS is used as MAC Address then the source host may end up sending packet to an INVALID IP.
Why can't WE USE MAC ADDRESSES AS IP ADDRESS ? Another Explanation....
Because they are permanent and if it is permanent then even if the host is not online ROUTERS will have to store it in memory. IPs are dynamic and the number of IPs in routing table depends upon the number of ONLINE hosts in the network. (DHCP does not assign IP to offline hosts). So the dynamic nature of IP helps in reducing the size of Routing table in Router's memory. So, IP Should always be DYNAMIC.
So, In conclusion :
IP is expected to be dynamic and MAC is supposed to be Static [Although, we can change it by changing the NIC or by MAC Spoofing but generally MACs do not change like IP Addresses and they are not expected to change for the reasons mentioned above.]
[IP GETS INVALID BECAUSE THE LEASE TIME EXPIRES FOR THE PARTICULAR HOST AS DHCP SERVER LEASES IP DYNAMICALLY TO HOST FOR CERTAIN PERIOD ONLY AFTER WHICH IT MAY TAKE IT BACK].
IP IS A SOFTWARE / LOGICAL NUMBER WHILE MAC IS PHYSICAL / HARD CODED / PERMANENT NUMBER.
Both of them have their own uses and we cannot use MAC address as IP address and IP Address as MAC address practically.
I hope it answers :)
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