Spring 2003 1

Ch 18 IP Addresses

2

Internet ProtocolInternet Protocol

Only protocol at Layer 3Defines

Internet addressingInternet packet formatInternet routing

3

IP AddressingIP Addressing

Independent of hardware addressingUsed by

Higher-layer protocolsApplications

IP address32-bit integerDotted decimal notation (e.g., 140.128.11.20)Each connection must be assigned one unique IP

address

4

IP Address DetailsIP Address Details

Divided into two partsPrefix identifies network (net ID)Suffix identifies host (host ID)

max. number of hostGlobal authority assigns unique prefix to

networkLocal administrator assigns unique suffix to

host

5

IP Address DetailsIP Address Details

140.128 163.23

.1.2 .5.8

140.128.1.1 163.23.1.8

Default gateway

.12.24 .12.23.5.2DNS

6

Original Classes of IP Addresses

Original Classes of IP Addresses

7

Dotted Decimal NotationDotted Decimal Notation

Four decimal values per 32-bit addressEach decimal number

Represents eight bitsIs between 0 and 255

8

Dotted Decimal NotationDotted Decimal Notation

Range for different classes of addresses Class A: 0.0.0.0 - 127.255.255.255 Class B: 128.0.0.0 - 191.255.255.255 Class C: 192.0.0.0 - 223.255.255.255 Class D: 224.0.0.0 - 239.255.255.255 Class E: 240.0.0.0 - 247.255.255.255

9

Addressing ExamplesAddressing Examples

10

Division of the Address Space

Division of the Address Space

10. x. y. z

24-bit7-bit

11

Subnet and Classless Addressing

Subnet and Classless Addressing

172.21.0.0

172.22.0.0

172.23.0.0

172.24.0.0172.25.0.0

Exhaust five class-B addresses

12

Subnet and Classless Addressing

Subnet and Classless Addressing

Subnetting

172.21

16 bits 8 bits

Class BHost Id

8 bits

X 0

Net Id Subnet Id

172.21.1.0

172.21.5.0

172.21.4.0

172.21.3.0172.21.2.0

13

Address MaskAddress Mask

Accompanies IP address32 bit binary value

Net ID = 172.21 Subnet ID

16 bits 8 bits

Class B Host ID

8 bits

Subnet mask 111…………….1 11……1 00…..0 = 255.255.255.0or 172.21.0.0 / 24

16 bits 10 bits

Class B Host ID

6 bits

Subnet mask 111…………….1 11……1 11 000000 = 255.255.255.192or 172.21.0.0 / 26

Net ID = 172.21 Subnet ID

14

CIDR NotationCIDR Notation

Uses slash notationExample

128.211.0.0/17

Means that the boundary between prefix and suffix occurs after the first 17 bits

15

IP Address AllocationIP Address Allocation– Static

• public IP address (by hand)• private IP address (via NAT, IP sharing)

– Dynamic• public IP address (via DHCP or relay agent)

16

Special AddressesSpecial Addresses

0.0.0.0140.128.0.0140.128.255.255255.255.255.255127.0.0.1

17

Special AddressesSpecial AddressesLoopback never leaves local computerMulti-homed hosts

A host that connects to multiple networks