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Part 5: CCNA Training: What is a Network

Posted: October 21st, 2016

CCNA TRAINING: THE NETWORK INTERFACE CARD AND BIA ADDRESS

There are a few ways to connect to a network for this moment we will concentrate on a wired only connection.

To connect to a network it is common to use a cable attached to a port on your P.C called an Ethernet port using an RJ45 connector.

Every interface has been assigned a unique address called a “Burned in Address” which identifies the interface uniquely on the network.

Every Frame which your device sends will include the unique BIA (Burned in Address) as a source address.

The BIA

The BIA is a 48bit value written in a format called “Hexidecimal” or just “Hex”

The BIA is made of two parts, the OUI (Organisational Unique Identifier) and the Vender Assigned Part. The 48bit BIA is split down the middle 24bits make up the OUI and 24bits define the Vendor assigned part.

The OUI identifies the manufacturer of the interface and is assigned to the maker by global standards body called the IEEE (Institute of Electrical and Electronics Engineers), more on this later.

To discover the MAC address of your own NIC (Network Interface Card) simply type in the following command into the command prompt of your machine:

Step 1: Go to start, type “cmd” in the box indicated by the red arrow, then hit the return key. A new screen will appear

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Step 2: Type into the command prompt the command “ipconfig /all” following by the return key. A series of messages will appear

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The machine used in this example has a unique MAC of “68-F7-28-33-2D-67” MAC address is shown is unique to this particular machine, it is expected that no other Ethernet interface in the entire world has the same address as this particular interface.

HEXIDECIMAL
All MAC address are written in HEX.
1. Each character in the MAC address is a HEX character.
2. Each HEX character is composed of 4 binary bits
3. These four bits are sometimes referred to a “Nibble”
4. Each Binary character in the 4 bit nibble has a value. The value of the binary bit is dependent on its position in the nibble.

 

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5. By changing the binary from off “0” to on “1” will cause the corresponding value to take effect
Example One:

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The binary bits with the values of 2 and 1 have been switched “on”, whilst the binary bits with the values of 8 and 4 have remained in the “off” position. The value of the four bits is 3

 

Example 2:

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The binary bits with the values of 8 and 1 have been switched “on”, whilst the binary bits with the values of 4 and 2 have remained in the “off” position. The value of the four bits is 9

Example 3:

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The binary bits with the values of 8 and 2 have been switched “on”, whilst the binary bits with the values of 4 and 1 have remained in the “off” position. The value of the four bits is 10

In HEX any value from 10 to 15 are not represented as the numerical value but are substituted with a letter, the table below show the correlation between the binary, value and letters

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Anatomy of a MAC address
Every MAC is made up of 48 bits. Each MAC address has two main parts:
1. The OUI = 24 bits
2. The Vendor assigned part = 24 bits

Say for example you wanted to get into the NIC market one of the very first things you would have to do is get a unique OUI (Organisational Unique Identifier), these are acquired for the IEEE. The IEEE is in charge of ensuring that each NIC card maker has a unique OUI.

The OUI is always the first 24 bits of the MAC address and the Vendor assigned part is always the second 24 bits. Recall that each character is HEX, and each HEX character is composed of 4 binary bits.

 

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It is the responsibility of the NIC manufacturer to ensure that they do not create NIC will duplicate MAC addresses and it is the responsibility of the IEEE to ensure that they do not assign the same OUI to multiple vendors