IP Tutorials

This tutorial explains IPv6 address, IPv6 address terminology, IPv6 address format, types of IPv6 address, moving to IPv6 and special IPv6 address including equivalent IPv4 address.

The current version of IP (known as version 4 or IPv4) has not changed substantially since Request for Comments (RFC) 791, which was published in 1981. IPv4 has proven to be robust, easily implemented, and interoperable. It has stood up to the test of scaling internetworks to a global utility the size of today’s Internet. This is a tribute to its initial design.
However, the initial design of IPv4 did not anticipate the following:

The recent exponential growth of the Internet and the impending exhaustion of the IPv4 address space

Given that an IP address is 32 bits in length, there are 232 actual IP addresses, which are 4.3 billion addresses. Only 3.7 billion of these are actually usable. Many addresses are reserved, such as the research (239–254), broadcast (255), multicast (224–239), private (10, 172.16, and 192.168), and loopback addresses (127). And, of course, many of the usable addresses are already assigned, leaving about 1.3 billion addresses for new growth. As a result, public IPv4 addresses have become relatively scarce, forcing many users and some organizations to use a NAT to map a single public IPv4 address to multiple private IPv4 addresses. Although NATs promote reuse of the private address space, they violate the fundamental design principle of the original Internet that all nodes have a unique, globally reachable address, preventing true end-to-end connectivity for all types of networking applications. Additionally, the rising prominence of Internet-connected devices and appliances ensures that the public IPv4 address space will eventually be depleted.

The need for simpler configuration

Most current IPv4 implementations must be either manually configured or use a stateful address configuration protocol such as 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.

The requirement for security at the Internet layer

Private communication over a public medium such as the Internet requires cryptographic services that protect the data being sent from being viewed or modified in transit. Although a standard now exists for providing security for IPv4 packets (known as Internet Protocol security, or IPSec. This standard is optional for IPv4 and additional security solutions, some of which are proprietary, are prevalent.

The need for better support for prioritized and real-time delivery of data

Although standards for prioritized and real-time delivery of data—sometimes referred to as Quality of Service (QoS)—exist for IPv4, real-time traffic support relies on the 8 bits of the historical IPv4 Type of Service (TOS) field and the identification of the payload, typically using a User Datagram Protocol (UDP) or Transmission Control Protocol (TCP) port.

Unfortunately, the IPv4 TOS field has limited functionality and, over time, has been redefined and has different local interpretations. The current standards for IPv4 use the TOS field to indicate a Differentiated Services Code Point (DSCP), a value set by the originating node and used by intermediate routers for prioritized delivery and handling.

Additionally, payload identification that uses a TCP or UDP port is not possible when the IPv4 packet payload is encrypted. To address these and other concerns, the Internet Engineering Task Force (IETF) has developed a suite of protocols and standards known as IP version 6 (IPv6).

Why Switch to IPv6

IPv6 solves the Address Depletion Problem

With the explosion in the popularity of the Internet has come the introduction of commerce related activities that can now be done over the Internet by an ever-increasing number of devices. With IPv4, the number of public addresses available to new devices is limited and shrinking. IPv4 cannot continue to scale and provide global connectivity to all of the planned Internet-capable devices to be produced and connected in the next 10 years. Although these devices can be assigned private addresses, address and port translation introduces complexity to the devices that want to perform server, listening, or peer functionality. IPv6 solves the IPv4 public address depletion problem by providing an address space to last well into the twenty-first century. The business benefit of moving to IPv6 is that mobile cell phones, personal data assistants (PDAs), automobiles, appliances, and even people can be assigned multiple globally reachable addresses. The growth of the devices connected to the Internet and the software that these devices run can proceed without restraint and without the complexity and cost of having to operate behind NATs.

IPv6 Solves the Disjoint Address Space Problem

With IPv4, there are typically two different addressing schemes for the home and the enterprise network.
In the home, an Internet gateway device (IGD) is assigned a single public IPv4 address and the IGD assigns private IPv4 addresses to the hosts on the home network.
An enterprise might have multiple public IPv4 addresses or a public address range and either assign public, private, or both types of addresses within the enterprise’s intranet.
However, the public and private IPv4 address spaces are disjoint; they do not provide symmetric reach ability at the Network layer. Symmetric reach ability exists when packets can be sent to and received from an arbitrary destination. With IPv4, there is no single addressing scheme that is applied to both networks that allows seamless connectivity. Connectivity between disjoint networks requires intermediate devices such as NATs or proxy servers. With IPv6, both homes and enterprises will be assigned global address prefixes and can seamlessly connect, subject to security restrictions such as firewall filtering and authenticated communication.

IPv6 Solves the International Address Allocation Problem

The Internet was principally a creation of educational institutions and government agencies of the United States of America. In the early days of the Internet, connected sites in the United States received IPv4 address prefixes without regard to summarize ability or need. The historical result of this address allocation practice is that the United States has a disproportionate number of public IPv4 addresses.
With IPv6, public address prefixes are assigned to regional Internet registries, which, in turn, assign address prefixes to other ISPs and organizations based on justified need. This new address allocation practice ensures that address prefixes will be distributed globally based on regional connectivity needs, rather than by historical origin. This makes the Internet more of a truly global resource, rather than a United States—centric one. The business benefit to organizations across the globe is that they can rely on having available public IPv6 address space, without the current cost of obtaining IPv4 public address prefixes from their ISP.

IPv6 Restores End-to-End Communication

With IPv4 NATs, there is a technical barrier for applications that rely on listening or peer based connectivity because of the need for the communicating peers to discover and advertise their public IPv4 addresses and ports. The workarounds for the translation barrier might also require the deployment of echo or rendezvous servers on the Internet to provide public address and port configuration information.
With IPv6, NATs are no longer necessary to conserve public address space, and the problems associated with mapping addresses and ports disappear for developers of applications and gateways. More importantly, end-to-end communication is restored between hosts on the Internet by using addresses in packets that do not change in transit.

IPv6 Uses Scoped Addresses and Address Selection

Unlike IPv4 addresses, IPv6 addresses have a scope, or a defined area of the network over which they are unique and relevant. For example,
IPv6 has a global address that is equivalent to the IPv4 public address and a unique local address that is roughly equivalent to the IPv4 private address.
Typical IPv4 routers do not distinguish a public address from a private address and will forward a privately addressed packet on the Internet.
An IPv6 router, on the other hand, is aware of the scope of IPv6 addresses and will never forward a packet over an interface that does not have the correct scope.

IPv6 Has More Efficient Forwarding

IPv6 is a streamlined version of IPv4. Excluding prioritized delivery traffic, IPv6 has fewer fields to process and fewer decisions to make in forwarding an IPv6 packet.
Unlike IPv4, the IPv6 header is a fixed size (40 bytes), which allows routers to process IPv6 packets faster. Additionally, the hierarchical and summarize able addressing structure of IPv6 global addresses means that there are fewer routes to analyze in the routing tables of organization and Internet backbone routers. The consequence is traffic that can be forwarded at higher data rates, resulting in higher performance for tomorrow’s high-bandwidth applications that use multiple data types.

IPv6 Has Support for Security and Mobility

IPv6 has been designed to support security (IPsec) (AH and ESP header support required) and mobility (Mobile IPv6) (optional). Although one could argue that these features are available for IPv4, they are available on IPv4 as extensions, and therefore they have architectural or connectivity limitations that might not have been present if they had been part of the original IPv4 design. It is always better to design features in rather than bolt them on. The result of designing IPv6 with security and mobility in mind is an implementation that is a defined standard, has fewer limitations, and is more robust and scalable to handle the current and future communication needs of the users of the Internet. The business benefit of requiring support for IPsec and using a single, global address space is that IPv6 can protect packets from end to end across the entire IPv6 Internet. Unlike IPsec on the IPv4 Internet, which must be modified and has limited functionality when the endpoints are behind NATs, IPsec on the IPv6 Internet is fully functional between any two endpoints.

IPv6 features

Very large address space

IPv6's large address space deals with global growth, where route prefixes can be easily aggregated in routing updates.


IP security (IPSec) is built into IPv6, whereas it is an awkward add-on in IPv4. With IPv6, two devices can dynamically negotiate security parameters and build a secure tunnel between them with no user intervention.


With the growth of mobile devices, such as PDAs and smart phones, devices can roam between wireless networks without breaking their connections. Streamlined encapsulation The IPv6 encapsulation is simpler than IPv4, providing faster forwarding rates by routers and better routing efficiency.

  • No checksums are included, reducing processing on endpoints.
  • No broadcasts are used, reducing utilization of devices within the same subnet.


Information is built into the IPv6 header, where a flow label identifies the traffic; this alleviates intermediate network devices from having to examine contents inside the packet, the TCP/UDP headers, and payload information to classify the traffic for QoS correctly.

Transition capabilities

Various solutions exist to allow IPv4 and IPv6 to successfully coexist when migrating between the two. One method, dual stack, allows you to run both protocols simultaneously on an interface of a device. A second method, tunneling, allows you to tunnel IPv6 over IPv4 and vice versa to transmit an IP version of one type across a network using another type. Cisco supports a third method, referred to as Network Address Translation-Protocol Translation (NAT-PT), to translate between IPv4 and IPv6 (sometimes the term Proxy is used instead of Protocol).

Stateless and Stateful Address Configuration

To simplify host configuration, IPv6 supports both stateful address configuration (such as address configuration in the presence of a DHCP for IPv6, or DHCPv6, server) and stateless address configuration (such as address configuration in the absence of a DHCPv6 server).

New Protocol for Neighboring Node Interaction

The Neighbor Discovery protocol for IPv6 is a series of Internet Control Message Protocol for IPv6 (ICMPv6) messages that manages the interaction of neighboring nodes (nodes on the same link). Neighbor Discovery replaces and extends the Address Resolution Protocol (ARP) (broadcast-based), ICMPv4 Router Discovery, and ICMPv4 Redirect messages with efficient multicast and unicast Neighbor Discovery messages.


IPv6 can easily be extended for new features by adding extension headers after the IPv6 header.

Moving to IPv6

One nice feature of moving your network to IPv6 is that you don't have to do it all in one step. Various migration strategies support both IPv4 and IPv6 as you migrate from the former to the latter.

Most common method for transition is given in following table.

Transition Method Description
Dual stacking

Devices such as PCs and routers run both IPv4 and IPv6, and thus have two sets of addresses.

Manual IPv6-over-IPv4 (6to4) tunneling

IPv6 packets are tunneled across an IPv4 network by encapsulating them in IPv4 packets. This requires routers configured with dual stacks.

Dynamic 6to4 tunneling

Allows IPv6 localities to connect to other IPv6 localities across an IPv4 backbone, such as the Internet, automatically. This method applies a unique IPv6 prefix to each locality without having to retrieve IPv6 addressing information from address registries or ISPs.

Intra-Site Automatic Tunnel Addressing Protocol (ISATAP) tunneling

Uses virtual links to connect IPv6 localities together within a site that is primarily using IPv4. Boundary routers between the two addressing types must be configured with dual stacks.

Teredo tunneling

Instead of using routers to tunnel packets, Teredo tunneling has the hosts perform the tunneling. This requires the hosts to be configured with dual stacks. It is commonly used to move packets through an IPv4 address translation device.

NAT Proxying and Translation (NAT-PT)

Has an address translation device translate addresses between an IPv6 and IPv4 network and vice versa.

Dual Stacking

In dual stacking, a device runs both protocol stacks: IPv4 and IPv6. Of all the transition methods, this is the most common one.

Dual stacking can be accomplished on the same interface or different interfaces of the device. Figure shows an example of dual stacking on a router, where Network A has a mixture of devices configured for the two different protocols, and the router configured in a dual stack mode. Older IPv4-only applications can still work while they are migrated to IPv6 by supporting newer APIs to handle IPv6 addresses and DNS lookups with IPv6 addresses.
dual stack

The main disadvantage of dual stacking on a segment is that devices configured using only one stack must forward their traffic to a dual-stacked device, such as a router, which must then forward the traffic back to the same segment using the other stack.

This is an inefficient use of bandwidth, but it does allow devices using both protocol stacks to coexist on the same network segment.