IP Addressing

Dotted Decimal and Binary explanation

IP Addressing

• IP Addresses can be notated in Dotted Decimal and/or Binary, but you must understand both

• Dotted Decimal is what we are familiar with– eg. 128.41.230.65

– To find out what the value of the dotted decimal octet is we must know what the binary format is

• Binary bits are shown by a “1” or a “0” – “1” indicates that the binary place is “on”

– “0” indicates that the binary place is “off”

IP Addressing

• IP addresses in dotted decimal contain 4 octets– Add up the number of “locations” contained by the dots

: xxx.xxx.xxx.xxx = 4 octets

– Each octet contains 8 binary bits that tell us what the value of the octet in the dotted decimal notation

Binary as it relates to the Octet

XXX.XXX.XXX.XXX

Each octet is made up of 8 binary bit “places”

Calculate 4 octets X 8 bits = 32 bits total

Binary Place Values

0 0 0 0 0 0 0 0

128 64 32 16 8 4 2 1

= 0

0 0 0 0 0 0 0 1 = 1

0 0 0 0 0 0 1 1 = 3

=255

0 1 0 0 0 0 1 1 = 67

1 0 0 0 0 0 0 0 =128

! Remember a binary bit is either on or off – “1” or “0” !

Converting Dotted Decimal to Binary

128.41.230.65Lets convert the dotted decimal address shown here to binary

Converting Dotted Decimal to Binary

Take the value of the first Octet

128

Binary would look something like this

1 0 0 0 0 0 0 0

! Remember the value of the first binary bit place is 128 and the first bit place is “turned on” !

Converting Dotted Decimal to Binary

Take the value of the second Octet

41

Binary would look something like this

0 0 1 0 1 0 0 1

! Remember the values of the bit places turned on – 32, 8, and 1 – 32+8+1=41 !

Converting Dotted Decimal to Binary

Take the value of the third Octet

230

Binary would look something like this

1 1 1 0 0 1 1 0

! Remember the values of the bit places turned on – 128, 64, 32, 4, and 2 – 128+64+32+4+2=230 !

Converting Dotted Decimal to Binary

Take the value of the forth Octet

65

Binary would look something like this

0 1 0 0 0 0 0 1

! Remember the values of the bit places turned on – 64, and 1 – 64+1=65 !

Converting Dotted Decimal to Binary

128.41.230.65The whole thing in binary would look like this

10000000.00101001.11100110.01000001

Now you Know how!!