In computer network use 3 type of addresses, i.e. each computer has 3 addresses IP, MAC and port number but why ? why 3 addresses not one ?!

Hi,

Every computer has its own identifiers like: IP, MAc, Port, Computer Name, Security ID, GUID and some else, why all of these, as the computer requires and uses each one of them in the exact phase like MAC is used in Layer2 communication, IP is used in L3, port is used in L4 etc, also these paramters are needed for each machine to be unique in a network.

HTH

Best Regards,

ip address is a logical address or a unique address of a pc on a network and mac is a physical address or a unique address of a particular machine and port numbers are used with different protocols of ip A port is always associated with an IP address of a host and the protocol type of the communication, and completes the destination or origination address of a communication session. A port is identified for each address and protocol by a 16-bit number, commonly known as the port

The question exactly reflects another question as below:

"Why did the ISO published the OSI model of7 layers? Why didn't they just squeeze the model into just4 layers and define one addressing scheme?".

The ISO should answer this question. We are just users who work on their inventions that are delivered to us as it is.

They all work at different layers of Internet protocol suite and therefore serves different purposes. MAC is assigned to the network card when it is shipped and works at the link layer. IP address is assigned usually by the user and works at the network layer. Packet forwarding is possible only through IP addresses as it is hierarchical while MAC addresses are not hierarchical and thus not support forwarding. Port numbers are used by protocols at the transport layer like TCP and UDP. The port number, added to a computer's IP address, completes the destination address for a communications session.

IP address is a numerical label assigned to a device participating in Network e.g computer,printer,etc

MAC address is a physical address that is unique for a device (computer) and port number is used for process to process communication.

These different address plays their own role i.e MAC address is resolved into IP address using DNS.

Layer 1 communication - access to media devices

(Services connect with transmission)

(protocol physicla structure)

(device is cables)

Layer 2 communication - Local network and host delivery 

(services is error freetransfer )

(protocl is PPP/SLIP)

(device NIC)

Layer 3 communication - Routing to Destination 

(Services is routing )

(protocol is IP,IPX,Apple talk)

(devices is router and l3 switches)

Layer 4 communication -delivering and sequencing 

(Host to host communation is application services)

(protocol is port numbers)

(Devices host and gateway)

Layer 5 communication - End to End communication or establishing connection 

(session establishment is services )

(Protocl netbios, SQL etc)

(devices host and gateway )

Layer 6 communication - Encrypting and formating and decrypting 

(data encryprtion and decrption is service and many more)

(Protocol JPEG ASCII TIF GIF etc) 

(Device host and  gateway)

Layer 7 communication - data genaration

(Internet Explorer Service is service)

(protocol user application / SMTP)

(device is host and gateway)

Hope this sound correct !!

MAC address also known as physical address assigned at data link layer of the OSI model

Every host has a unique MAC address which cant be changed..

Ip address is the address asigned to all devices in the network taking part in communication using Internet Protocol..IP address identifies the network interface and performs local addressing..

Port Numbers is always associated with the IP address and protocol in the specific communication..

Based on the types of services ,IP address and protocol used by the host ,port number varies..IP s like TCP and UDP use port numbers for clinet server communication..

the above hierarchy of addresses are due to the proposed layered architecture of Internet, as suggested by both OSI and TCP/IP

A thorough understanding of the Layered approach of the OSI Model with explain more about the MAC, IP and Port numbers addressing.

while the MAC address is a physical address operating in the Layer2 Datalink layer of the OSI model, in a network that does not require packet switching there will be no need for IP  addresses, because IP addresses is a logical address that occur in the network layer for packet switching while port numbers are used to identify unique processes in the SEssion layer. Port allows unique establishment of processes.

I fully agree with all answers