Hardware & Logical Addressing

Hardware Addressing :

The hardware address is used by devices to communicate on the local

network. Hardware addressing is a function of the data-link layer of the OSI model (Layer-2).

The hardware address for Ethernet networks is the MAC address, a 48-bit

hexadecimal address that is usually hard-coded on the network card. This means the MAC address cannot be altered; however, the MAC

address is often stored in flash on the NIC, and thus can be changed with

special utilities.

MAC addresses can be represented in two formats (either notation is

acceptable):

00:43:AB:F2:32:13

0043.ABF2.3213

The MAC address has one shortcoming – it contains no hierarchy. There is

no mechanism to create boundaries between networks. Instead, the first six hexadecimal digits of a MAC identify the manufacturer of the network card (referred to as the OUI (Organizational Unique Identifier)), and the last 6 digits identify the host device (referred to as the host ID). Still, there is no way to distinguish one network from another.

Image the difficulties this poses. If only hardware addressing existed, all

devices would technically be on the same network. Modern internetwork

systems like the Internet could not exist, as there would be no way to

separate my network from your network.

Furthermore, imagine if the entire Internet was a purely switched, data-link

layer environment. Switches, as a rule, forward broadcasts out all ports.

Guesstimating that there are billions devices on the Internet, with each

device sending out a broadcast on average every few seconds, the resulting broadcast storms would be devastating. The Internet would simply collapse.

Logical Addressing :

 

Logical addressing is a function of the network layer of the OSI Model

(Layer-3).

Logical addresses, unlike hardware addresses, provide a hierarchical

structure to separate networks. A logical address identifies not only a unique Host ID, but also the network that host belongs to. Additionally, logical addresses are rarely hard-coded onto hosts, and can be changed freely.

Two common logical addressing protocols are IPX (Internetwork Packet

Exchange) and IP (Internet Protocol). IPX was predominantly used on

Novell networks, but is mostly deprecated. IP is the most widely-used

logical address today. Internet Protocol (IP) was developed by the Department of Defense (DoD) during the late 1970’s. It was included in a group of protocols that became known as theTCP/IP protocol suite.

The DoD developed their own networking model to organize and define the

TCP/IP protocol suite. This became known as the DoD Model, and consists of four layers:

IP provides two core functions:

Logical addressing of hosts

Routing of packets between networks.

IP has undergone several revisions. IP Version 4 (IPv4) is currently in

widespread deployment, but will eventually be replaced with IP Version 6

(IPv6).

To be continued......