Internet Protocol Version 6 (IPv6) and Internet Communication

An Introduction to the IPv6 Protocol

The current version of the Internet Protocol (known as IP version 4 or IPv4) has not been substantially changed since 1981, when the Internet Engineering Task Force (IETF) published the definitive specification of IP (RFC 791). IPv4 has proven to be robust, easily implemented, and interoperable. It has stood the test of scaling an internetwork to a global utility the size of today's Internet, which is a tribute to the protocol’s initial design.

The initial design, however, did not anticipate the exponential growth of the Internet and the exhaustion of the IPv4 address space, or the effort required to maintain routing information. Because of the way in which IPv4 network IDs are allocated, there are routinely over 70,000 routes in the routing tables of Internet backbone routers. Most current IPv4 implementations are configured either manually or through a stateful address configuration protocol such as the Dynamic Host Configuration Protocol (DHCP). With more computers and devices using IP, there is a need for a simpler and more automatic configuration of addresses and other configuration settings that do not rely on the administration of a DHCP infrastructure.

Another factor driving the development of IPv6 is the need for improved security. Private communication over a public medium like the Internet requires encryption services that protect the data sent from being viewed or modified in transit. There is a standard for providing security for IPv4 packets (known as Internet Protocol security or IPSec). In IPv4, however, this standard is optional and proprietary solutions are prevalent. In IPv6, IPSec support is required. To address these concerns, the IETF has developed a suite of protocols and standards known as IP version 6 (IPv6). This new version incorporates the concepts of many proposed methods for updating the IPv4 protocol.

For the latest set of RFCs and Internet drafts describing IPv6 and IPv4 coexistence and migration technologies, see the Internet Engineering Task Force (IETF) Web site at: (Web addresses can change, so you might be unable to connect to the Web site or sites mentioned here.)

Benefits and Purposes of the IPv6 Protocol

An IPv6 address is four times as large as an IPv4 address. The global addresses used on the IPv6 portion of the Internet are designed to create an efficient, hierarchical, and summarized routing infrastructure that addresses the common occurrence of multiple levels of Internet service providers. On the IPv6 Internet, the backbone routers have an efficient and hierarchical addressing and routing infrastructure that uses smaller routing tables.

IPv6 supports both stateful address configuration (such as address configuration in the presence of a DHCP server) and stateless address configuration (address configuration in the absence of a DHCP server). The support for IPSec is an IPv6 protocol suite requirement. This requirement provides a standards-based solution for network security needs and promotes interoperability between different IPv6 implementations.

The new format of the IPv6 header is designed to minimize header validation and processing. In addition, a new field in the IPv6 header helps to define how traffic is handled and identified for quality of service delivery.

IPv6 can be extended for new features by adding extension headers after the IPv6 header. Unlike the IPv4 header, which can only support 40 bytes of options, the size of IPv6 extension headers is only constrained by the size of the IPv6 packet. The new Neighbor Discovery protocol in IPv6 is a series of Internet Control Message Protocol for IPv6 (ICMPv6) messages that manage the interaction of neighboring nodes. Neighbor Discovery replaces Address Resolution Protocol (ARP), ICMPv4 Router Discovery, and ICMPv4 Redirect messages with efficient multicast and unicast messages. The following table compares the key features of the IPv4 and IPv6 protocols.

Comparison of Features in IPv4 and IPv6



Source and destination addresses are 32 bits (4 bytes) in length.

Source and destination addresses are 128 bits (16 bytes) in length.

IPSec support is optional.

IPSec support is required.

No identification of packet flow for Quality of Service (QoS) handling by routers is present within the IPv4 header.

Packet flow identification for QoS handling by routers is included in the IPv6 header using the Flow Label field.

Fragmentation is done by both routers and the sending host.

Fragmentation is not done by routers, only by the sending host.

Header includes a checksum.

Header does not include a checksum.

Header includes options.

All optional data is moved to IPv6 extension headers.

Address Resolution Protocol (ARP) uses broadcast ARP Request frames to resolve an IPv4 address to a link layer address.

ARP Request frames are replaced with multicast Neighbor Solicitation messages.

Internet Group Management Protocol (IGMP) is used to manage local subnet group membership.

IGMP is replaced with Multicast Listener Discovery (MLD) messages.

ICMP Router Discovery is used to determine the IPv4 address of the best default gateway and is optional

ICMP Router Discovery is replaced with ICMPv6 Router Solicitation and Router Advertisement messages and is required.

Broadcast addresses are used to send traffic to all nodes on a subnet.

There are no IPv6 broadcast addresses. Instead, a link-local scope all-nodes multicast address is used.

Must be configured either manually or through DHCP.

Does not require manual configuration or DHCP.

Uses host address (A) resource records in the Domain Name System (DNS) to map host names to IPv4 addresses.

Uses host address (AAAA) resource records in the Domain Name System (DNS) to map host names to IPv6 addresses.

Uses pointer (PTR) resource records in the INADDR.ARPA DNS domain to map IPv4 addresses to host names.

Uses pointer (PTR) resource records in the IP6.ARPA DNS domain to map IPv6 addresses to host names.