IPv6 Essentials: What You Need to Know About the New Version

Do We Really Need a New IP Version?

Living in a world where nearly every household has more than one computer, imagine the number of IP addresses required for them. Likewise, more and more IP telephones and IP television sets are being introduced around the world, ensuring that the public IP address range will eventually be exhausted. The Network Address Translator (NAT) has been implemented to provide a temporary solution to the scarce number of IP addresses.

Under these circumstances, the answer is: “YES” we definitely need a new, evolved, IP version; one that is more flexible, scalable, and adaptable to the growth and changes of the Internet. This new version of IP is IPv6 and extensive details on this can be found in IETF RFCs 2460 through 2466.

So what can we expect from the new IP version? Here’s what IPv6 has to offer:

  • Billions of addresses with no possibility of exhaustion
  • Ability to lighten the burden of huge routing tables
  • Provide extra security features
  • Simplify the routing process
  • Allow efficient and accurate Quality of Service options
  • Support possible future evolution
  • Provide interoperability between old and new version

Main Features and Improvements in IPv6

  • Simpler Header Format – IPv6 contains only eight fields, compared to fourteen fields in IPv4, making its processing faster and consequently improving throughput.
  • Longer Address Space – Source and destination addresses are sixteen bytes long each, versus four bytes in IPv4, which eliminates the shortage on IP addressing space.
  • Hierarchical Addressing Scheme – IPv6 provides a more efficient addressing scheme which decreases the huge number of routing entries in backbone routers with its efficient summarization capability.
  • Built-in Security – Data integrity and authentication are assured in IPv6 with the use of IPSec.
  • Better QoS support – A completely new 20-bit field in the IPv6 header is used to identify different traffic flows between a source and destination, and apply the necessary policies appropriately.
  • Extensibility – At the end of the IPv6 header, various extended options can be supported, making it possible for extensions to be easily adaptable.

IPv4 and IPv6 Header Comparison

IPv4 Header

IPv4 Header

IPv6 Header

IPv6 Header

After taking a closer look at the diagrams of headers for IPv4 and IPv6, here’s a rundown of the main differences:

  • IPv6 header consists of 40 octets in contrast to the 20 octets in IPv4.
  • Seven fields in IPv4 (marked with light blue shading) are not used in IPv6.
  • Three field names (marked in light green shading) are kept the same from IPv4 to IPv6.
  • Four fields (marked in light yellow) have changed names and position from IPv4 to IPv6.
  • One completely new field is incorporated in IPv6 (Flow label field).

IPv6 Header Details Include:

  • Version – A 4-bit field that is always 4 in IPv4 and 6 in IPv6.
  • Traffic class – This field is similar to the ToS field in IPv4 and it is used for Differentiated services classification.
  • Flow label – This is a new 20-bit field that is designed for differentiating traffic flows.
  • Payload length – Similar to Total Length field in IPv4, shows how many bytes follow the 40-byte header of IPv6.
  • Next Header – Identifies the upper layer protocol, similar to the Protocol field in IPv4.
  • Hop Limit – The concept of this field is similar to the TTL field in IPv4, which is to indicate the maximum number of hops a packet can traverse before being dropped.
  • Source address – 16-bytes address identifying the source address of the packet.
  • Destination address – 16-bytes address identifying the destination address of the packet.
  • Extension headers – These are optional headers that can be used to provide extra information.

All About IPv6 Addresses

IPv6 addresses are written in eight groups of four hexadecimal digits with colons separating each group like so:

  • 2000:0000:0000:0000:0457:ACFD:45CB:230B

First leading zeros within a group can be omitted. For example 0457 can be written as 457. Also, successive groups of zero bits can be replaced by a pair of colons as “::”. This substitution can only take place one time in an address. Using the above example: 2000:0000:0000:0000:0457:ACFD:45CB:230B can be replaced with:2000::457:ACFD:45CB:230B.

In a compressed IPv6 address representation, to be able to resolve its fully qualified representation, you can count the number of groups in the compressed address, subtract this number from 8, and then multiply the result by 16. The result will be the number of bits represented by the “::”.

For example, in the address 2000::457:ACFD:45CB:230B, there are five blocks. The number of bits expressed by the “::” is 48 or (8 – 5) x 16. Each group is represented by 16 bits, hence 3 (48/16) groups of leading “zeros” are represented by the “::”.

The difference IPv6 address types include:

  • Unicast – one-to-one
  • Multicast – one-to-many
  • Anycast – one-to-nearest

Note: Broadcast address scheme is not defined in IPv6; broadcasting as known in IPv4 is performed using multicast address in IPv6.

Unicast address type is the most common IP address type that is assigned to individual interfaces. It is divided into various types of unicast addresses according to their purpose. The most important ones are: IPv6 Global Unicast Addresses, Link-Local Addresses, and Special Addresses. Details about these addresses can be found in RFC 2373.

IPv6 Global Unicast Addresses are also known as Aggregatable Global Unicast Addresses, identified by the Format Prefix of 2000::/3 through E000::/3, with the exception of FF00::/8. These addresses are equivalent to public IPv4 addresses. By default, the number of bits used to identify the subnet is 64 and the number of bits used to identify the host on the subnet is again 64. At the ISP, or organization boundaries, these addresses can be aggregated hence limiting routing table entries.

The 64-bit host identifier in an IPv6 address is derived from the underlying link layer address (MAC address) of an interface. For mapping of MAC addresses into Interface identifiers in IPv6 global unicast and other addresses, Extended Universal Identifier (EUI) is used. The 64-bit EUI format is derived from the 48-bit MAC address by inserting the hexadecimal number FFFE (16 bits) between the upper 3 bytes and the lower 3 bytes of the MAC address, and setting the 7th bit of the leftmost byte to 1.

To Sum It All Up …

The benefits from IPv6 are huge. Although it’s a new technology, it is expected to grow exponentially and eventually completely replace IPv4. The new IPv6 is able accomplish more for several reasons:

  • It makes NAT and its drawbacks obsolete
  • It covers the IP addressing needs of every IP device on the planet
  • It’s ideal for supporting new generation services
  • Supports mobility
  • Provides security
  • Serves in the greater extend the strict quality requirements of broadband services

The transformation to IPv6 will not be completed overnight. It will take some years during which coexistence of IPv4 and IPv6 will be common, however IPv6 will eventually dominate.

 in Cisco


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