© 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved. © The McGraw-Hill Companies, Inc.

Subnet Design and IP Addressing

Asst. Prof. Chaiporn Jaikaeo, Ph.D. chaiporn.j@ku.ac.th

http://www.cpe.ku.ac.th/~cpj Computer Engineering Department

Kasetsart University, Bangkok, Thailand

Adapted from the notes by Lami Kaya and lecture slides from Anan Phonphoem

2

Outline

IP Address

CIDR

3

Internet Addresses

Internet protocol must hide physical network details

Application doesn’t care about physical

Need address to communicate without knowing underlying network of each other

Address should be

Unique

Uniform addressing scheme

Independent to physical networks

Network

D.L.

P.L.

D.L.

P.L.

Network

D.L.

P.L.

D.L.

P.L.

4

Internet Model Revisited

Application

Transport

Network

Data Link

Physical

Application

Transport

Network

Data Link

Physical

Transmission medium

sender router

router

receiver

Network Layer Revisited

Network 1

Network 6

Network 5

1.1 1.2

6.6

6.1

6.3

5.7

5.2

Network 3 3.8

3.3 Router

Data 1.1 5.7

1.1, 1.2, 6.1, 5.7, ... are logical addresses

R1

R3 R2

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IP Addressing Scheme

Unique 32-bit binary number (4 bytes)

Assigned to each network interface

Used for identify host and communicate

Two-level hierarchical address

prefix (network ID) – assigned globally

suffix (Node/host ID) – assigned locally

Address must be coordinated globally

Network ID Host ID

Prefix Suffix

7

Internet Classes

Traditional addressing scheme

Classful Addressing

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IP Address Classes

A 50%

B 25%

C 12.5%

D E

10

No. of Networks / Hosts

11

IP address in decimal notation

27 26 25 24 23 22 21 20

0 0 0 0 1 0 1 1

8 + 2 + 1 = 11

x x x x x x x x

13

Class ranges of Internet Address

14

IP address in decimal notation

www.ku.ac.th

15

Class A example

16

Class C example

17

Network Address

18

Internet Example

Network and Host addresses

A Network with Two Levels of Hierarchy

Network -> Host

19

20

A Network with Three Levels of Hierarchy

Network -> Subnet -> Host

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Addresses with and without Subnetting

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Classful Subnet Masks

Class Binary Dotted-Decimal CIDR

Notation

A 11111111 00000000 00000000 00000000 255.0.0.0 /8

B 11111111 11111111 00000000 00000000 255.255.0.0 /16

C 11111111 11111111 11111111 00000000 255.255.255.0 /24

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Subnet Masks

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Example: Subnet Mask

Find the network ID of each of the following hosts with specified subnet masks:

IP: 192.168.5.3 Mask: 255.255.255.0

IP: 172.130.10.20 Mask: 255.255.255.0

IP: 192.168.10.5 Mask: 255.255.255.128

IP: 158.108.228.178 Mask: 255.255.240.0

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Outline

IP Address

CIDR

26

Classless Inter-Domain Routing

CIDR - Classless Inter-Domain Routing

Introduced in 1993 to replace classful network design in the Internet

To slow the growth of routing tables on routers

To help slow the rapid exhaustion of IPv4 addresses

No longer restrict network addresses as one or more 8-bit groups

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CIDR Notation

Specifies mask with prefix size

More convenient than binary representation

Example:

NetID: 158.108.0.0 Subnet Mask: 255.255.0.0

CIDR notation: 158.108.0.0/16

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CIDR Host Address

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Example: CIDR Notation

Convert mask to corresponding prefix size

255.0.0.0

255.192.0.0

255.255.255.252

Convert prefix size to corresponding mask

/8

/12

/16

/20

/28

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Example: CIDR Notation

Find the network ID of each of the following hosts with specified prefix size:

IP: 192.168.5.3/24

IP: 172.130.10.20/18

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Special IP Addresses

Network Address all hosts = 0; e.g. 158.108.0.0/16

Directed Broadcast Address Broadcast to a specified network all hosts = 1; e.g. 158.108.255.255/16

Limited Broadcast Address Broadcast to local network all 1; e.g. 255.255.255.255

This computer Address all 0; e.g. 0.0.0.0

Loopback Address 127.0.0.0/8 127.x.x.x

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Loopback Addresses

Allow programmers to test the program logic quickly without needing two computers and without

sending packets across a network

During loopback testing no packets ever leave a computer the IP software forwards packets from one

application to another

The loopback address never appears in a packet traveling across a network

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Loopback Addresses

โปร เซส A โปร เซส A

/

Physical

127.0.0.1

โปร เซส A Process A

TCP/UDP

IP

Data Link

Loopback Interface

127.0.0.1

Other Addresses

Process B

Incoming packet to Loopback Interface

Outgoing packet from Loopback to Process

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Directed Broadcast Address

Use for sending to all nodes in class range

Class A broadcast example:

10.255.255.255

Class B broadcast example:

158.108.255.255

Class C broadcast example:

202.100.15.255

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Special IP Address

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Example: Subnet Design

You are given an IP address block

12.6.8.0/24

You want to divide this block into subnets

Subnet A to serve 28 hosts

Subnet B to serve 40 hosts

Subnet C to serve 70 hosts

List the designed subnets with the following information

(1) subnet ID, (2) mask, (3) first usable address, (4) last usable address, (5) directed broadcast address

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Example: Subnet Design

Design subnetting scheme

Subnet C (70 hosts)

Subnet A (28 hosts)

Subnet B (40 hosts)

Original /24 block

(256 addrs)

/25 block (128 addrs)

/26 block (64 addrs)

/26 block (64 addrs)

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Example: Subnet Design

Create summary table

Subnet SubNet ID Subnet Mask First Host IP Last Host IP Broadcast Addr

C 12.6.8.0 255.255.255.128 12.6.8.1 12.6.8.126 12.6.8.127

A 12.6.8.128 255.255.255.192 12.6.8.129 12.6.8.190 12.6.8.191

B 12.6.8.192 255.255.255.192 12.6.8.193 12.6.8.254 12.6.8.255