SUBNETTING AN IPV4 NETWORK

9.1.3J U D D M AV E R I C K TA N B S E C E - 4

SUBNET

Or sub-network is a product of segmenting a network into smaller network spaces

MASKIs used to determine what SUBNET an IP address belongs to.SUBNET

MASKis a screen of numbers used for routing traffic within a subnet.

SUBNET

255.255.255.0

SUBNET MASK

PREFIX

192.168.1.0/25

CLASS

1ST OCTET

DECIMAL RANGE

NETWORK/HOST ID

DEFAULT SUBNET MASK

A 1-126 N.H.H.H 255.0.0.0

B 128-191 N.N.H.H 255.255.0.0

C 192-223 N.N.N.H 255.255.255.0

D 224-239 RESERVED FOR MULTICASTING

E 240-254 EXPERIMENTAL

Dotted Decimal Dotted Binary

Address 192.168.1.0 11000000.10101000.00000001.00000000

Mask 255.255.255.0 11111111.11111111.11111111.00000000

Class A addresses 127.0.0.0 to 127.255.255.255 cannot be used and is reserved for loopback and diagnostic functions.

Prefix: /248 8 811111111.11111111.11111111.00000000

Conversion: Subnet mask/ PrefixNETWORK PORTION HOST PORTION

Dotted Decimal Dotted Binary

Address 192.168.1.0 11000000.10101000.00000001.00000000

Mask 255.255.255.0 11111111.11111111.11111111.00000000

192.168.1.0/24 network

Dotted Decimal Dotted Binary

Address 192.168.1.0 11000000.10101000.00000001.0 0000000

Mask 255.255.255.0 11111111.11111111.11111111.0 0000000

NETWORK PORTION HOST PORTION

NETWORK PORTION HOST PORTION

Subnetting Borrowed

Calculating: Number of Subnets = 2B ; B = number of bits borrowed = 21 = 2 subnets

Calculating: Number of Valid Hosts Per subnet = 2H - 2; H = number of bits for host portion ; -2 = for network id and broadcast addresses

= 27 -2 = 62 valid host addresses per subnet

Dotted Decimal Dotted Binary

Address 192.168.1.0 11000000.10101000.00000001.0 0000000

Mask 255.255.255.128 11111111.11111111.11111111.1 0000000

NETWORK PORTION HOST PORTION

Borrowed192.168.1.0/25 network

Increment Number/ “Magic Number = binary value of rightmost ‘1’ among borrowed bits

= 28 = 128

Subnets : X.X.X.0- X.X.X.1 - X.X.X.126 -X.X.X.127 X.X.X.128- X.X.X.129 - X.X.X.254 -X.X.X.255Network Id Valid Host Add. Range Broadcast Add.