How to break down a mac address? - CCENT

Raymond Mason

Lets say I had this MAC address: 84-3A-4B-C8-E9-00

I broke that down to decimals and I got: 132-58-75-200-233-0

How do I find the first 24 bits? How do I even take the decimals I got and put them into bits?

Out of the first 24 bits how do I find where the I/G, G/L and OUI is?

clarson

it is better to just use the hex digits.

each hex digit is 4 bits.  24 bits / 4 = 6 hex digits.  so the first 24 bits are the first 6 hex digits or, in your case, 84-3A-4B.  Or the first half of the MAC address as the MAC address is 48 bits in length

the I/G is the 8th bit in the first octet.  the first octet is 0x84 or 1000 0100.  the 8th bit is zero.
the g/l is the 7th bit of the first octet.  and from above it is also zero.

5th   0
6th   1
7th   0  <- g/l bit
8th   0  <- i/g bit

and the OUI is the first 24 bits. and from above is 84-3A-4B

kaiju

Convert the MAC from hex to binary instead of hex to decimal.

0 = 0000

1 = 0001

2 = 0010

3 = 0011

4 = 0100

5 = 0101

6 = 0110

7 = 0111

8 = 1000

9 = 1001

A = 1010

B = 1011

C = 1100

D = 1101

E = 1110

F = 1111

So 84-3A-4B-C8-E9-00 converts to 10000100-00111010-0100101-11001000-11101001-00000000 with the portion in bold being the OUI. The remaining answers can be derived from the conversion.

Raymond Mason

Thank you so much you guys. I really appreciated your feedback.