What is an Addressing Scheme ?
- An addressing scheme is obviously a requirement for communications in a computer network.
- An addressing scheme, packets are forwarded from one place to another.
- Each of the three layers, 2, 3, and 4, of the TCP/IP protocol stack model produces a header, as indicated in below diagram.
- In this figure, host 1 communicates with host 2 on a network of seven nodes, R1 through R7, and a payload of information encapsulated in a frame by the link layer header, the network layer header, and the transport layer header is carried over a link.
- Within any of these three headers, each source or destination is allocated an address as identification for the corresponding protocol layer.
- The three types of addresses are summarized as follows.
- Link layer (layer 2) address
- Network layer (layer 3) address
- Transport layer (layer 4) address
Link layer (layer 2) address:
- A 6-byte (48-bit) field called Media Access Control (MAC) address that is signified by a 6-field hexadecimal number, such as 89-A1-33-2B-C3-84, in which each field as taken as two bytes long.
- Every interface has a unique MAC address. Every input or output of a networking device has an interface to its connected link.
- Normally, the same MAC address doesn’t share two interfaces then only safe. Both MAC addresses of a source interface and a destination interface contains by link layer header.
Network layer (layer 3) address:
- A 4-byte (32-bit) field called Internet Protocol (IP) address that is signified by a 4-field dot-separated number, such as 220.127.116.11, in which each field is taken as one byte long.
- An IP address can be known worldwide at the network level.
- A network layer header contains both IP addresses of a source node and a destination node.
Transport layer (layer 4) address:
- A 2-byte (16-bit) field called port number that is characterized by a 16-bit number, such as 4,892. The port numbers identify the two end hosts’ ports in a communication.
- Any host can be running several network applications at a time and thus each application needs to be identified by another host communicating to a targeted application.
- For example, source host 1 requires a port number for communication to uniquely identify an application process running on the destination host 2.
- A transport layer header contains the port numbers of a source host and a destination host, as seen in the figure. Note that a transport-layer “port” is a logical port and not an actual or a physical one, and it serves as the end-point application identification in a host.