IP Subnetting

IP Addressing Introduction

• IPv4 addresses are 32 bits in length.• IPv4 broken into four bytes (called octets), with a

dot between each byte.• Classes of Addresses

Class A1 - 126

Used for network

Class B128 - 191

Class C192 - 223

Class D224 - 239Multicast

Class E240 - 254Future

Decimal to Binary Numbers

IP Address Components

• IP address has two part, the first part is the network which identifies the network where the system is connected, and a second part is the Host which identifies that particular system on the network.

Subnet Mask

Guidelines for IP Addressing

• You must not use 127 for the first octet of the network ID. This value is reserved for diagnostic purposes.

• You must not use all 1s (binary) for the host ID. If all bits are set to 1, the address is interpreted as a broadcast address.

• You must not use all 0s for the host ID. If host bits are set to 0, some TCP/IP implementations interpret this as a subnetwork address.

• You must not duplicate host IDs within a network segment.

Identifying IP Addresses

• Determine which of the following IP addresses is valid or invalid

131.107.256.80Invalid (256)

222.222.255.222Valid

127.1.1.1Invalid (127)

198.121.254.255Invalid (Broadcast)

What Is a Subnet?

• A subnet is a physical segment of a network that is separated from the rest of the network by a router or routers.

• A network of multiple subnets connected by routers is often referred to as an internetwork.

Creating a Subnet

How many subnets?2X = number of subnets you need (X represents subnet

bits)

How many hosts per subnet? 2Y - 2 = number of hosts (Y represents host bits)

What are the valid subnets?256 – subnet mask

What’s the broadcast address for each subnet?

What are the valid hosts? Valid hosts are the numbers between the subnets, omitting all the 0s and all 1s.

Example 1192.168.10.0 = Network address

255.255.255.192 = Subnet mask• How many subnets? Since 192 is 2 bits on (11000000),

the answer would be 22.• How many hosts per subnet? We have 6 host bits off

(11000000), so the equation would be 26 – 2 = 62 hosts.• What are the valid subnets? 256 – 192 = 64. Remember,

we start at zero and count in our block size, so our subnets are 0, 64, 128, and 192.

• What’s the broadcast address for each subnet? The number right before the value of the next subnet is all host bits turned on and equals the broadcast address.

Example 1

• What are the valid hosts?

The subnets064128192

The first host165129193

The last host62126190254

The broadcast address63127191255

Example 2

• 192.168.10.0 = Network address• 255.255.255.224 = Subnet maskHow many subnets? 224 is 11100000, so our equation

would be 23 = 8.

How many hosts? 25 – 2 = 30.

What are the valid subnets? 256 – 224 = 32. We just start at zero and count to the subnetmask value in blocks (increments) of 32: 0, 32, 64, 96, 128, 160, 192, 224.

What’s the broadcast address for each subnet (always the number right before the next subnet)?

What are the valid hosts (the numbers between the subnet number and the broadcast address)?

Example 2

• What are the valid hosts?

The subnets0326496128160192224

The first host1336597129161193225

The last host306294126158190222254

The broadcast

address316395127159191223255

Exercise 1

• You are given a Class C network (192.168.1.0) and you have 4 segments in your network, where the largest segment has 50 hosts. What subnet mask should you use and what is the layout of your addresses?

Answer 1

• Subnet Mask = 255.255.255.192

The subnets064128192

The first host165129193

The last host62126190254

The broadcast address63127191255

Exercise 2

• You are given the following address: 192.168.1.63/29. What type of address is this network, broadcast, or host?

• Answer: -

• This is a broadcast address.

Exercise 3

• You are given the following address: 172.16.4.255/22. What type of address is this network, broadcast, or host?

• Answer: -• This is a host address.

VLSM