IPv4 addressing scheme has some major limitations and they are:

• Limited space and The IPv4 specifies a 32 bits (4,294,967,296 possible addressable nodes) address field and these address field is rapidly running out.
• Lack of security

To overcome the above limitations they implemented the IPv6 and the IPv6 specifies a 128 bits (~3.4*1038 possible addressable nodes) and this IPv6 provides a large space when compared to IPv4 and the requirement of large space is because the global network in rapid growth by introducing the new technologies like internet, mobile users, consumer devices & network devices.

Apart from satisfying the limitations of IPv4, IPv6 have the following features:
• Performance has been increase
• Ease-to configure
• Managing the network issues

The design of the header field in IPv6 is different from the IPv4 and the below figure shows the differences between the IPv4 and IPv6 header fields.

IPv4 and IPv6 Difference

Figure: Difference between the IPv4 and IPv6 header fields.

The security Improvements over IPv4 are

The one of the major limitation in IPv4 is the lack of security and the IPv6 protocol has solved some but not all the security problems which is found in IPv4
• Makes the port scanner harder due to the massive size of the address space.
• In IPv6 the security is provided in between end-to-end(workstation/host) to destination(workstation/host).
Cryptographically General Address (CGA): This CGA provides additional security IPv6 neighborhood router discovery mechanism and The IPv6 allows the users to get proof of ownership for a particular IPv6 address and it allows the messages with the owners private key.
• Through this CGA the spoofing attacks will not possible and stealing of IPv6 address is much harder.
• IP Security or IPsec which is used to provides the high network level security and cryptographically based security services through the use of this two protocols namely AH(Authentication header) and ESP(Encapsulated Security Payload)header.

The authentication header (AH) is used to provide the data authentication and data integrity and also it provides the Anti-replay protection.

The Encapsulated Security Payload (ESP) header is used to provide the confidentiality and or the authentication and in the ESP header these confidentiality and authentication are optional and we have to select at least one of the services and in the ESP header, the authentication is applied to only the data being encrypted.

The Authentication header and Encapsulated Security Payload (ESP) header can be used separately or in combination to provide desired security and the below figure shows how the data is encapsulated in IPv6 packet.

IPv6 Network Data Encapsulation

The organizations cannot changed to IPv6 by the overnight, IPv6 is gradually deployed and the IPv4 will be supported for legacy clients and servers but the IPv6 is a step forward when compare to the IPv4.The design of IPv6 brings the improvement in both functionality and security.