**Valid IP Address**

- must be in the form of A.B.C.D,
- where A, B, C, and D are numbers from 0-255
- The numbers cannot be 0 prefixed unless they are 0.

**Subnetting** – the process of taking a large network and splitting it up into many individual smaller subnetworks or subnets.

Address classes give us a way to break the total global IP space into discrete networks.

Network ID – used to identify networks

Host ID – used to identify individual hosts.

Subnet ID

10.0.1.10 (10.0 is the network ID, 1.10 is the host ID)

In a world with subnetting, some bits that would normally comprise the host ID are actually used for the subnet ID.

**Subnet Masks** – 32-bit numbers that are normally written out as four octets in decimal

IP Address | 9 | 100 | 100 | 100 |

IP Address (in binary) | 0000 1001 | 0110 0100 | 0110 0100 | 0110 0100 |

Subnet Mask (in binary) | 1111 1111 | 1111 1111 | 1111 1111 | 0000 0000 |

Each part of the IP Address is an ** octet**, which means that it consists of eight bits.

The number 9 in binary is just 1001, but since each octet needs eight bits, we need to pad it with some zeros in front.

The size of a subnet is defined by the subnet mask.

A single 8-bit number can represent 256 different numbers, or more specifically, the number 0-255.

**9.100.100.100, with subnet mask 255.255.255.224**

- Since that subnet mask represents
**27 ones followed by five zeros**, a quicker way of referencing this is with the notation /27. The entire IP and subnet mask could be written out as 9.100.100.100/27.

## Basic Binary Math

0 or 1, binary or base 2

### Binary

32 | 16 | 08 | 04 | 02 | 01 |

1 | |||||

1 | 0 | ||||

1 | 1 | ||||

1 | 0 | 0 | |||

1 | 0 | 1 | |||

1 | 1 | 0 | |||

1 | 1 | 1 | |||

1 | 0 | 0 | 0 | ||

1 | 0 | 0 | 1 | ||

1 | 0 | 1 | 0 | ||

1 | 0 | 1 | 1 |

### Decimal

10 | 01 |

1 | |

2 | |

3 | |

4 | |

5 | |

6 | |

7 | |

8 | |

9 | |

1 | 0 |

1 | 1 |

8\;bit\;is\;2^8 = 256

4\;bit\;is\;2^4 = 16

16\;bit\;is\;2^16\ = 65536

decimal – base 10

binary – base 2

**In binary:**

0 + 0 = 0 |

0 + 1 = 1 |

1 + 0 = 1 |

1 + 1 = 10 |

The basic equation is x or y = z. If either x or y is true, then z is true, otherwise, it’s false.

In Binary, 1 or 0 = but 0 or 0 equals 0. 1 and 1 = 1, but 1 and 0 = 0, 0 and 0 = 0.