1. Subnet Design and IP Addressing
Asst. Prof. Chaiporn Jaikaeo, Ph.D.
Computer Engineering Department
Kasetsart University, Bangkok, Thailand
Adapted from the notes by Lami Kaya and lecture slides from Anan Phonphoem
© 2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved.
© The McGraw-Hill Companies, Inc.

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

4. Internet Model Revisited
router
sender
router
receiver
Application
Transport
Network
Data Link
Physical
Application
Transport
Network
Data Link
Physical
Network
D.L.
P.L.
Network
D.L.
P.L.
Transmission medium

5. Network Layer Revisited
Data
1.1
5.7
1.1, 1.2, 6.1, 5.7, ... are logical addresses
1.1
1.2
Network 1 R1
6.1
Network 6
6.6
6.3 R3 R2
5.2
Router
3.3
Network 5
5.7
Network 3
3.8

6. 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

8. IP Address Class

9. IP Address Classes B
25% A
50% C
12.5% D E

10. No. of Networks / Hosts

11. IP address in decimal notation x
= 11

12. Example: IP address practice
Binary
Dotted Decimal #1 #2 #3

13. Class ranges of Internet Address

14. IP address in decimal notation

15. Class A example

16. Class C example

17. Network Address

18. Internet Example
Network and Host addresses

19. A Network with Two Levels of Hierarchy
Network -> Host

20. A Network with Three Levels of Hierarchy
Network -> Subnet -> Host

21. Addresses with and without Subnetting

22. Classful Subnet Masks Class Binary Dotted-Decimal CIDR Notation A /8 B
/16 C
/24

23. Subnet Masks

24. Example: Subnet Mask
Find the network ID of each of the following hosts with specified subnet masks:
IP: Mask:
IP: Mask:
IP: Mask:
IP: Mask:

25. 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

27. CIDR Notation Specifies mask with prefix size Example:
More convenient than binary representation
Example:
NetID: Subnet Mask:
CIDR notation: /16

28. CIDR Host Address

29. Example: CIDR Notation
Convert mask to corresponding prefix size
Convert prefix size to corresponding mask /8
/12
/16
/20
/28

30. Example: CIDR Notation
Find the network ID of each of the following hosts with specified prefix size:
IP: /24
IP: /18

31. Special IP Addresses Network Address Directed Broadcast Address
all hosts = 0; e.g /16
Directed Broadcast Address
Broadcast to a specified network
all hosts = 1; e.g /16
Limited Broadcast Address
Broadcast to local network
all 1; e.g
This computer Address
all 0; e.g
Loopback Address
/8  127.x.x.x

32. 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

33. Loopback Addresses โปร เซส โปร โปร เซส เซส / A A A Loopback Interface
Process A
โปร
โปร
เซส
เซส A A A
Process B
Outgoing packet from
Loopback to Process
TCP/UDP /
Loopback Interface IP
Incoming packet
to Loopback Interface
Data Link
Physical
Other Addresses

34. Directed Broadcast Address
Use for sending to all nodes in class range
Class A broadcast example:
Class B broadcast example:
Class C broadcast example:

35. Special IP Address

36. Example: Subnet Design
You are given an IP address block
/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

37. Example: Subnet Design
Design subnetting scheme
Subnet C (70 hosts)
/25 block (128 addrs)
Original /24 block (256 addrs)
Subnet A (28 hosts)
/26 block (64 addrs)
Subnet B (40 hosts)
/26 block (64 addrs)

38. Example: Subnet Design
Create summary table
Subnet
SubNet ID
Subnet Mask
First Host IP
Last Host IP
Broadcast Addr C A B