NETWORK LAYER

IP Addressing

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ANNOUNCEMENT: Rescheduled NO PRACTICAL SESSIONS ON

TUESDAY 22, November 2010 Rescheduled sessions: MONDAY:

November 21, 2010, NW202 PRAC GROUP 1: 13.00 – 14.00 --- PRAC GROUP 2: 15.00 – 16.00 PRAC GROUP 3: 16.00 – 17.00 PRAC GROUP 4: 17.00 – 18.00

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Review - Local Area Networks

So far, we have only discussed local area networks (LAN), Underlying physical medium is shared. Data sent to a LAN goes to ALL of the

computers on that LAN. The size of LANs is limited.

An electrical signal can only travel a limited distance.

LAN size can be extended by using Repeaters

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Review - Wide Area Network (WAN)

Network that covers large geographic area

A Wide Area Network (WAN) is made up from interconnected LANs

Network devices such as Switches or Routers can be used to join LANs together to form a WAN Any examples? Internet…

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802.3 LAN

Cat5 UTP

WAN

ISP

Router

TCP/IP Protocol Stack

Two computers, anywhere in the world can communicate, even when not directly connected.

TCP/IP - a suite of protocols, is the reference model that provides specifications for the Internet IP protocol operates at

Layer 3 or Internet/ Network layer

TCP works at Layer 4

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TCP

IP

Protocol

Network Layer

Network layer is responsible for moving data through a set of networks (Figure 1).

Router (R) helps to connect different networks together A, B, C, D are different

networks (Figure 1) IP protocol operates at

Network Layer IP protocol uses IP

Address to identify a PC uniquely in the Internet.

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R

R

R - Router

R R

R

RR

Figure 1

Figure 1

Network Addressing: Analogy with telephone numbers

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Network addresses are similar to Phone numbers Area Code / Phone Number 831 – 479-5783

Network address helps to identify path (route) through network cloud from start to destination. Each network (red ring in the

figure 2) has an address 1.0 as 1 is the common

number between 1.1, 1.2, 1.3 Each host (PC) within the

network has an address (blue ring), e.g., 1.3

Router

Figure 2

Figure 1

Why two Addresses for computer on network?

Both Layer 2 (Ethernet) and Layer 3 (IP) Addresses are needed:

Layer 2 / MAC address Physically burned into the

NIC Doesn’t change The device’s real identity

Layer 3 / Protocol address Configurable

Can be changed The device’s “mailing”

address Needs to change when

device is moved connected to a network

having different network address

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Review: What is the MAC and IP Address on my computer?

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Flat versus Hierarchical10

Layer 2 - Flat addressing schemes Next available Social Security Number MAC addresses

Layer 3 - Hierarchical addressing schemes Phone numbers ZIP codes IP addresses

IP Addresses11

Older Technology - Classful IP Addressing Defines IP address as belonging to one

of the available five classes: Class A Class BClass C Class DClass E

Current technology - Classless IP Addressing

IP Address12

IP Addresses are 32 bits.

Divide into four 8 bit sections (octets).

Convert from binary to decimal.

Classful IP Addressing13

Five different classes of IP addresses A, B, C, D, E

Class A, B and C are primary classes Used for assigning IP addresses

Class D, E used for special purposes Class D for multicast

E.g., Videoconferencing Class E addresses are reserved for

experimentation

IP Address Classes14

Network ID Host ID

Network ID Host ID

8 16

Class A

32

Class B 10

Class C110

Multicast AddressesClass D1110

Reserved for experimentsClass E

1111

248

Look at the first group of numbers in the dotted decimal notation

Class Range A 0-127 B 128-191 C 192-223 D 224-239 E 240-255

Which Class has the largest Host ID and how many bits long?

Which class has the largest Network ID and how many bits long?

Subnet mask - NetID /HostID boundary

Every machine on the network must know which part of the host address will be used as netid and hostid. Subnet mask identifies

the boundary between netid and hostid

Which class has more hosts?

Which class supports more networks?

Default subnet masks are Class A : 255.0.0.0 Class B : 255.255.0.0 Class C : 255.255.255.0

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Network Host Host Host

Network Network Host Host

Network Network Network Host

1st octet 2nd octet 3rd octet 4th octet

Class A

Class B

Class C

Find Network/Host ID from IP Address

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Logical ‘AND’ IP address and subnet mask to get Net-ID. E.g. IP address is 192.24.134.23, Find Network ID

using default subnet mask of 255.255.255.0 for class C Find the binary representation of IP address and

subnet mask Logical ‘AND’ with subnet mask

11000000.00011000.10000110.00010111 IP Address 11111111.11111111.11111111.00000000 Subnet mask for

Class C 11000000.00011000.10001010.00000000 Network ID

Convert binary to decimal value Network ID: 192.24.134.0

AND

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Hierarchy in IP addressing

• IP addresses are hierarchical.• Conceptually each IP address is a pair

• Divided into a prefix and a suffix– Prefix (net-id) identifies network to which

computers are attached.– Suffix (host-id) identifies computers within

that network.

RD-CSY1017-07/08

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Loopback address 127.0.0.0

Network address IP address with all host bits set to 0

Example: 172.16.0.0, subnet mask:255.255.0.0 Broadcast address

IP address with all host bits set to 1 Example: 172.16.255.255, subnet

mask:255.255.0.0

Special IP Addresses

RD-CSY1017-07/08 19

Private IP Addresses

Private IP Addresses cannot exist on the public Internet.

Name Address Translation (NAT) used to give data packets a “legitimate” IP source address.

Class B: 172.16.0.0 to 172.31.0.0

(In the 3rd Octet, the 128, 64, and 32 bit are off. The 16 bit is on.)

Class C: 192.168.0.0 to 192.168.255.0

(256 separate Class C Addresses)

Class A: 10.0.0.0(Favored by large enterprises because of its flexibility)

Grouping Devices into Networks and Hierarchical Addressing

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Divide a large network into subnetworks Geographical area Functionality

Departments Admin, HR…

IP addressing example21

223.1.1.1

223.1.1.2

223.1.1.3

223.1.1.4 223.1.2.9

223.1.2.2

223.1.2.1

What is the class of IP address in the figure?

Which network device is connecting the two networks?

Subnet Masks – Your Turn!22

Underline the network portion of each address:

Network Address Subnet Mask

172.0.0.0 255.0.0.0

172.16.0.0 255.255.0.0

192.168.1.0 255.255.255.0

192.168.0.0 255.255.0.0

192.168.0.0 255.255.255.0

10.1.1.0 /24

10.2.0.0 /16

10.0.0.0 /16

What is the other portion of the address?

Subnet Masks – Your Turn!23

Underline the network portion of each address:

Network Address Subnet Mask

172.0.0.0 255.0.0.0

172.16.0.0 255.255.0.0

192.168.1.0 255.255.255.0

192.168.0.0 255.255.0.0

192.168.0.0 255.255.255.0

10.1.1.0 /24

10.2.0.0 /16

10.0.0.0 /16

What is the other portion of the address? Host Addresses