Title - Seminar - IP Version 6 title


IP version 6 (IPv6) is a new version of the Internet Protocol based on IPv4. Its designed to be an evolutionary step from the current IPv4 and will interoperate with IPv4 equipment allowing for a gradual and piecemeal introduction into the network. Major Changes from IPv4 are:

  • Addresses enlarged from 32 to 128 bits

  • Allow mobility of computers

  • Guaranteed Quality of Service for connections

  • Direct support for security protocols (encryption, network)

  • Evolutionary migration to enable functions

There are a number of reasons that IPv6 is needed: there is a shrinking pool of available IP addresses, the accumulation of changes to IPv4 has made it very cumbersome, new applications and devices do not fit into the original assumptions about the IP network, and there is a great deal more need for security of data transmissions.

IPv6 supports large hierarchical addresses that will allow the Internet to continue to grow and provide new routing capabilities not built into IPv4. It has a new concept of an Anycast addresses which can be used so that the message finds its way through the network along a particular route such as ensuring that the packet stays within a single ISPs network. It also has a "local use address" mechanisms allowing for communications within a small area and not taking valuable public addresses.

The changes from IPv4 to IPv6 fall primarily into the following categories:

  • Expanded Routing and Addressing Capabilities
    IPv6 increases the IP address size from 32 bits to 128 bits, to support more levels of addressing hierarchy and a much greater number of addressable nodes, and simpler auto-configuration of addresses.

  • A new type of address called an "Anycast address" is defined to identify sets of nodes where a packet sent to an Anycast address is delivered to one of the nodes. The use of Anycast addresses in the IPv6 source route allows nodes to control the path that their traffic flows.

  • Header Format Simplification
    Some IPv4 header fields have been dropped or made optional, to reduce the common-case processing cost of packet handling and to keep the bandwidth cost of the IPv6 header as low as possible despite the increased size of the addresses. Even though the IPv6 addresses are four time longer than the IPv4 addresses, the IPv6 header is only twice the size of the IPv4 header.

  • Quality-of-Service Capabilities
    A new capability is added to enable the labeling of packets belonging to particular traffic "flows" for which the sender requests special handling, such as non-default quality of service or "real- time" service.

  • Authentication and Privacy Capabilities
    IPv6 includes the definition of extensions that provide support for authentication, data integrity, and confidentiality. This is included as a basic element of IPv6 and will be included in all implementations.

The Technical Aspects of IPv6

A comparison of the fields in the IPv4 packet header vs. the IPv6 fields is shown in Figure 1.

Figure 1. Comparison of IPv4 packet header with IPv6


In both IPv4 and IPv6, there may be optional headers appearing after the main header and before the data. Most IPv6 extension headers are not examined or processed by any router along a packet's delivery path until it arrives at its final destination. IPv6 extension headers can be of arbitrary length. The format of the IPv6 packet is shown below in Figure 2 .

Figure 2. IPv6 Packet Format


Ver 4-bit Internet Protocol version number = 6.

Prio 4-bit Priority value.

Flow Label 24-bit field. See IPv6 Quality of Service section.

Payload Length 16-bit unsigned integer. Length of payload, i.e., the rest of the packet following the IPv6 header, in octets.

Next Hdr 8-bit selector. Identifies the type of header immediately following the IPv6 header. Uses the same values as the IPv4 Protocol field.

Hop Limit 8-bit unsigned integer. Decremented by 1 by each node that forwards the packet. The packet is discarded if Hop Limit is decremented to zero.

Source Address 128 bits. The address of the initial sender of the packet.

Destination Address 128 bits. The address of the intended recipient of the packet (possibly not the ultimate recipient, if an optional Routing Header is present).

The IPv6 extension headers that are currently defined are:

Routing Extended Routing (like IPv4 loose source route).

Fragmentation Fragmentation and Reassembly.

Authentication Integrity and Authentication. Security

Encapsulation Confidentiality.

Hop-by-Hop Option Special options which require hop by hop processing.

Destination Options Optional information to be examined by the destination node.

IPv6 Addressing

Unlike IPv4 addresses that refer to a node, IPv6 addresses are 128-bits long and are identifiers for individual interfaces. A node may be referenced by any of that node's interface. A single interface may be assigned multiple IPv6 addresses of any type.

There are three types of IPv6 addresses. These are unicast, anycast, and multicast. Unicast addresses identify a single interface. Anycast addresses identify a set of interfaces such that a packet sent to a anycast address will be delivered to one member of the set. Multicast addresses identify a group of interfaces is delivered to all of the interfaces in that group. There are no broadcast addresses in IPv6, their function being superseded by multicast addresses.

IPv6 Routing

Routing in IPv6 is almost identical to IPv4 routing under CIDR except that the addresses are 128- bit IPv6 addresses instead of 32-bit IPv4 addresses. With very straightforward extensions, all of IPv4's routing algorithms (OSPF, RIP, IDRP, ISIS, etc.) can used to route IPv6.

IPv6 also includes simple routing extensions that support powerful new routing functionality. These capabilities include:

  • Provider Selection (based on policy, performance, cost, etc.)

  • Host Mobility (route to current location)

  • Auto-Readdressing (route to new address

IPv6 Quality-of-Service Capabilities

The Flow Label and the Priority fields in the IPv6 header may be used by a host to identify those packets for which it requests special handling by IPv6 routers, such as non-default quality of service or "real-time" service. This capability is important in order to support applications which require some degree of consistent throughput, delay, and/or jitter. This type of application are commonly described as "multi- media" or "real-time" application.

Flow Labels

The 24-bit Flow Label field in the IPv6 header may be used by a source to identify those packets requiring special handling by the IPv6 routers. This is used to provide Quality of Service for real-time applications.
There may be multiple active flows from a source to a destination, as well as traffic that is not associated with any flow. A flow is uniquely identified by the combination of a source address and a non- zero flow label. Packets that do not belong to a flow carry a flow label of zero.


The 4-bit Priority field in the IPv6 header enables a source to identify the desired delivery priority of its packets, relative to other packets from the same source. The Priority values are divided into two ranges: Values 0 through 7 are used to specify the priority of traffic for which the source is providing congestion control, i.e., traffic that "backs off" in response to congestion, such as TCP traffic. Values 8 through 15 are used to specify the priority of traffic that does not back off in response to congestion, e.g., "real-time" packets being sent at a constant rate.

For congestion-controlled traffic, the following Priority values are recommended for particular application categories:

0 Uncharacterized traffic
1 "Filler" traffic (e.g., netnews)
2 Unattended data transfer (e.g., email)
3 (Reserved)
4 Attended bulk transfer (e.g., FTP, HTTP, NFS)
5 (Reserved)
6 Interactive traffic (e.g., telnet, X)
7 Internet control traffic (e.g., routing protocols, SNMP)

For non-congestion-controlled traffic, the lowest Priority value (8) should be used for those packets that the sender is most willing to have discarded under conditions of congestion (e.g., high-fidelity video traffic). The highest value (15) should be used for those packets that the sender is least willing to have discarded (e.g., low-fidelity audio traffic).

Transition to IPv6

There is a significant amount of equipment installed around the world that operate using IPv4. The reality of IPv6 is that it must continue to operate with IPv4 equipment without disruption. Since its not feasible to upgrade the entire world network, IPv6 devices does allow the IPv4 devices to be present anywhere in the network and still provide its advanced capabilities.

The IPv6 allows the transition from IPv4 through mechanisms allowing for a smooth transition. Some of the assumptions of the IPv6 are:

  • Incremental upgrade and deployment. Individual IPv4 hosts and routers may be upgraded to IPv6 one at a time without requiring any other hosts or routers to be upgraded at the same time. New IPv6 hosts and routers can be installed one by one.

  • Minimal upgrade dependencies. The only prerequisite to upgrading hosts to IPv6 is that the DNS server must first be upgraded to handle IPv6 address records. There are no prerequisites to upgrading routers.

  • Easy Addressing. When existing installed IPv4 hosts or routers are upgraded to IPv6, they may continue to use their existing address. They do not need to be assigned new addresses.

  • Low start-up costs. Little or no preparation work is needed in order to upgrade existing IPv4 systems to IPv6, or to deploy new IPv6 systems.

The mechanism for transitioning is:

  • An IPv6 addressing structure that embeds IPv4 addresses within IPv6 addresses, and encodes other information used by the transition mechanisms.

  • A model of deployment where all hosts and routers upgraded to IPv6 in the early transition phase are "dual" capable (i.e. implement complete IPv4 and IPv6 protocol stacks).

  • The technique of encapsulating IPv6 packets within IPv4 headers to carry them over segments of the end-to-end path where the routers have not yet been upgraded to IPv6.

  • The header translation technique to allow the eventual introduction of routing topologies that route only IPv6 traffic, and the deployment of hosts that support only IPv6.

It is likely that the first deployments will be in large corporate networks since the benefits of IPv6 are most suitable and cost effective for this group. This will be followed by large backbone systems, and then migrating to edge routers that access the networks. Small business and home users may the last to participate in the migration to IPv6.

More Information

In Summary:

  • IPv6 provides solutions for the increasing the available address, allows mobile nodes, provides better Quality of Service, and increases security.

  • IPv6 is compatible with todays IPv4 networks and there should be a smooth migration o IPv6.

  • Corporate networks and central node routers will be upgraded first followed by other network elements.


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