InetAddress class

The InetAddress class refers to the IP address, both IPv4 and IPv6.An instance of an InetAddress consists of an IP address and possibly its corresponding hostname. It provides a method to get the IP address of the hostname and hostname of the IP address. An IP address represents a 32 bit or 128-bit unsigned number. The InetAddress class represents a cache to store successful as well as the unsuccessful hostname.

TCP/IP Protocol

TCP/IP refers to the suite of communication protocols used to interconnect network devices on the Internet. TCP/IP applies to the data exchanges between end-to-end communications over the internet. It indicates how it should be broken into packets, addressed, transmitted, routed, and received at the destination. There are two main protocols in the suite that serve specific functions.

TCP specifies a way applications can create channels of communication across a network. It also specifies how a message assembles into smaller packets before they transmit over the Internet and reassembles in the right order at the destination address.

IP refers to how to address and route each packet to make sure it reaches the right destination. The gateway computer on the network checks this IP address to determine where to forward the message.

IP Address

An IP address is a numerical representation that uniquely identifies a specific resource on the network. IP address specifies the IPv4 and IPv6.

Addresses in IPV4 are 32-bits long, which allows for a maximum of 232 unique addresses. IPv6 has a 128-bits address, which provides 2128 unique addresses.

IP addresses indicate in binary numbers but are typically expressed in decimal form (IPv4) or hexadecimal form(IPv6) for making them more accessible to humans.

IP versions      

IPv4 addresses

The IPv4 protocol has 232 addresses. Addresses in IPv4 are 32-bits long and to create a maximum of 4,294,967,296 unique addresses. IPv4 is 32- bit binary numbers, contain two sub-addresses, the network and the host with an imaginary boundary separating both network and host. An IP address specifies as 4 octets of numbers from 0-255 represented in decimal form. An IPv4 address specifies in dotted-decimal notation, with every eight bits (octet) represented by a number from 1 to 255, each separated by a dot. An example of an IPv4 address looks like this: 192.168.17.43.

IPv4 addresses are composed of two parts. The first number in the address specifies the network, while the second number specifies the host. A network host denotes the computer connected to a computer network. A host specifies to the server offering information resources, services, and applications to users or other nodes on the network. It is a network that uses the various protocols and attaches the various hosts for their inter-communications.

Addressing modes of IPv4

  • Unicast Addressing mode

The data will be sent only to one intended host and the destination.

  • Broadcast Addressing Mode

The packet will be sent to all the hosts in a network segment.

  • Multicast Addressing mode

Multicast Addressing mode has a combination of both the previous two modes. The server sends packets that are entertained by more than one server. The network has one IP address for the Network Number, which represents the network, and one IP address is for the Broadcast address, which represents all the hosts in that network.

Classes of the IPv4

  • Class A

In Class A network, the first eight bits represent the network part of the address, while the remaining part of the address is the host part of the address. There are128 possible Class A networks. Class A has an address range 0.0.0.0 to 127.0.0.0

  • Class B

In Class B network, the network part of the address is represented by the first 16 bits, and the remaining part is referred to as the host part of the address. It has range from 128.0.0.0 to 191.255.0.0. There are near about 16,384 Class B networks.

  • Class C

In Class C network, the first 24 bits of the address represent the network address, and the remaining part denotes the host address. Class C has network addresses range from 192.0.0.0 to 223.255.255.0. There are near about 2 million possible Class C networks.

  • Class D

In Class D network uses for multicasting applications. It has 32-bit network addresses, represents to the multicast groups in the range of 224.0.0.0 ———239.255.255.255. Within the Class D address space, there are no host addresses.

  • Class E

In Class E networks having the addresses from 240.0.0.0 to 255.255.255.255. Its usage was never defined as this class is reserved. Due to this, most network implementations discard these addresses as illegal or undefined. The 255.255.255.255 address is considered as an exception, which is used as a broadcast address.

IPv4 address exhaustion

Initially, IPv4 specification was designed for the DARPA network. At the time, the 232 addresses were certainly considered sufficient. It became apparent that the IPv4 address space would not be big enough for a worldwide Internet with numerous connected devices per person. This will lead to the generation of the IPv6 addresses.

 IPv6 addresses

To avoid the address space issue in technology, IPV6 created an enormous address space for the network. The address space increases from IPv4 32 bits to IPv6 128 bits having 3.4*1038 (2128) unique addresses, which is reportedly enough addresses to assign one to every single atom on the surface of the earth. IPv6 specifies eight sets of four hexadecimal digits, which is separated by a colon. IPv6 address looks like 2DAB:FFFF:0000:3EAE:01AA:00FF:DD72:2C4A.There are no defined classes in the IPv6 version.

Addressing modes of IPv6

  • Unicast addressing mode

     The IPv6 packet consists of source and destination IP addresses.

The host has an IP address that is unique in that network segment. Whenever a network router receives a unicast IP packet, destined to a single host, it sends out one of its outgoing interface which connects to that particular host.

  • Multicast addressing mode

The packet destined to multiple hosts sends on a special multicast address. All the host’s interest in that multicast information, need to join that multicast group first. All the interfaces which are involved in that group receive the multicast packet and process it, while other hosts not interested in multicast packets ignore the multicast information.

  • Anycast addressing mode

Multiple hosts are assigned the same Anycast IP address. When a host wants to communicate with a host equipped with an Anycast IP address, it sends a Unicast message. By using the complex routing mechanism, that Unicast message delivers to the host closest to the sender in terms of routing cost.

Name Resolution

To remember the IP address of every device is not possible in both the case of both IPv4 and IPv6.The name resolution is a way of reconciling an IP address to a user-friendly computer domain name. The Domain Name Servers consists of a directory of domain names and translate them to Internet Protocol (IP) addresses. Although domain names are easy to remember, access websites based on IP addresses are accessible.

Whenever a client writes a web address www.google.com, your DNS associated with the domain name translates it into a machine-friendly IP address and directs your Internet connection to the correct website.

Methods of InetAddress

The InetAddress class doesn’t have public constructors, so you create a new instance by using one of its factory methods.

Factory methods: These methods are static methods in a class which return an instance of that class

Method Description
  public  static InetAddress getByName(String host) It creates an InetAddress object based on the provided hostname.
   public static InetAddress getByAddress(byte[] addr) It returns an InetAddress  object from a byte array of the raw IP address.
  public static getAllByName(String host) It returns an array of InetAddress objects from the specified hostname, as a hostname can be associated with several IP addresses.
public static InetAddress  getLocalHost() It returns the instance of InetAddress containing the local hostname and address.

Methods of InetAddress class:

Method Description
public  byte[] getAddress() It returns the raw IP address of this InetAddress object as an array.
public String getHostAddress() It returns IP address in textual form.
public boolean isAnyLocalAddress() It returns true if this address represents a local address.
public boolean isLinkLocalAddress() It returns true if this address is a link local address.
public boolean isLoopbackAddress() It returns true if this address is a loopback address.
public boolean isMCGlobal() It used to check whether the  multicast address has a global scope or not
public boolean isMCLinkLocal() It is used to check utility routine if the multicast address has a link scope or not.
public boolean isMCNodeLocal() It is used to check the utility routine if the multicast address has node scope or not.
public boolean isMCOrgLocal() It is used to check utility routine if the multicast address has organization scope or not.
public boolean isMCSiteLocal() It returns true if this multicast address has site scope.
public boolean isMulticastAddress() It returns true if this address is an IP multicast address.
public boolean isSiteLocalAddress() It returns true if this address is a site local address.
public int hashCode() It returns the hashcode associated with this address object.
public boolean equals(Object obj) It returns true if this IP address is the same as that of the object specified.

Example 1:  To get the localhost address of the system.

The output of the above program:

localhost address of the system

Example 2: List all IP address associate with a given hostname/domain.

The output of the above program:

IP address associate with a given hostname

Example 3: To check two IPs are equal or not by using equals() method.

The output of the program:

To check two IPs are equal or not by using equals() method.

Example 4: Using the various methods of the InetAddress class.

The output of the above program:

Using the various methods of the InetAddress class.

Example 5: The toString() method of InetAddress class converts the IP address to a String.  

The output of the program:

method of InetAddress class converts the IP address to a String.

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