Internet Addressing

1
Chapter 3

• Internet Addressing

2
Chapter 3 Outline

• Hosts
• Internet addresses
• Next Generation Internet
• IPv4
• Class A,B and C addresses
• Domain Name System (DNS)
• Creating InetAddresses
• Java 1.4 Added Methods
• Getter Methods
• Address Types
• Object Methods
• Chapter 3 Highlights

3
Hosts

• Devices connected to the Internet are called
  hosts
• Most hosts are computers, but hosts also include
  routers, printers, fax machines,etc.

4
Internet addresses

• Every host on the Internet is identified by a
  unique, four-byte Internet Protocol (IP) address.
  
• This is written in dotted quad format like
  199.1.32.90 where each byte is an unsigned
  integer between 0 and 255.
• There are about four billion unique IP addresses,
  but they arent very efficiently allocated

5
Next Generation Internet

• The solution is IPv6 which uses 128 bit addresses
• Improves services such as multicasting and secure
  communication
• Not yet widely deployed by ISPs
• Well written Java software should move to IPv6
  without modification/recompilation this is one
  benefit of abstracted APIs

6
IPv4

• Each 32 bit IP number consists of two components
• The network address
• The unique international address of the network
• The host address
• The unique address of a specific host in the net
• There are three classes of network address
  denoted class A, B and C

7
Class A,B and C addresses
192 . 85 . 35 . 87
0...
10...
110...
Network Address Byte
Host Address Byte
8
Domain Name System (DNS)

• Numeric addresses are mapped to names like
  www.msn.com or mail.msn.com by DNS.
• Each site runs domain name server software that
  translates names to IP addresses and vice versa
• DNS is a distributed system

9
IP Addresses and Java

• Java has a class java.net.InetAddress which
  abstracts network addresses
• Serves three main purposes
• Encapsulates an address
• Performs name lookup (converting a host name into
  an IP address)
• Performs reverse lookup (converting the address
  into a host name)

10
Creating InetAddresses

• There are no public InetAddress() constructors.
  Arbitrary addresses may not be created.
• All addresses that are created must be checked
  with DNS

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Ways to create InetAddress objects

• public static InetAddress getByName(String host)
  throws UnknownHostException
• public static InetAddress getAllByName(String
  host) throws UnknownHostException
• public static InetAddress getLocalHost() throws
  UnknownHostException

12
Java 1.4 Added Methods

• Java 1.4 adds two more factory methods that do
  not check their addresses with the local DNS
  server. The first creates an InetAddress object
  with an IP address and no hostname. The second
  creates an InetAddress object with an IP address
  and a hostname.
• public static InetAddress getByAddress(byte
  address) throws UnknownHostException
• public static InetAddress getByAddress(String
  hostName, byte address) throws
  UnknownHostException

13
Getter Methods

• They return the hostname as a string and the IP
  address as both string and a byte array
• public String getHostName()
• public byte getAddress()
• public String getHostAddress()

14
Address Types

• Public boolean isAnyLocalAddress()
• Public boolean isLoopbackAddress()
• Public boolean isLinkLocalAddress()
• Public boolean isSiteLocalAddress()
• Public boolean isMulticastAddress()
• Public boolean isMCGloabl()
• Public boolean isMCNodeLocal((
• Public boolean isMCLinkLocal()
• Public boolean isMCSiteLocal()
• Public boolean isMCOrgLocal()

15
Object Methods

• Public boolean equals (Object o)
• Public int hashCode ()
• Public String toString ()

16
Inet4Address and Inet6Address

• Public final class Inet4Address extends
  InetAddress
• Public final class Inet6Address extends
  InetAddress

17
Using InetAddress objects
import java.net.InetAddress import
java.net.UnknownHostExcepion public static void
main(String args) try InetAddress
inet1 InetAddress.getByName("asp.ee.
uwa.edu.au") System.out.println(
"HostAddress" inet1.getHostAddress())
InetAddress inet2
InetAddress.getByName("130.95.72.134")
System.out.println("HostName"
inet2.getHostName()) if (inet1.equals(inet2
)) System.out.println("Addresses are
equal") catch (UnknownHostException uhe)
uhe.printStackTrace()
18
Chapter Highlights

• In this chapter, you have learned
• About the Domain Name System (DNS) and domain
  name suffixes (such as .com)
• About the structure of an IP address and the
  various classes of IP addresses
• About the InetAddress class and its various
  methods