Migrating to an IPv6 Internet


(T) Between the Internet Protocol version 4 (IPv4) and version 6 (IPv6), IPv5 defined in RFC 1819 was intended for streaming traffic but has never widely been used. IPv6 was designed mainly to address space exhaustion and Internet backbone routing issues. IPv6 can be seen as a conservative extension to IPv4. Most application-layer protocols do not need major changes to support IPv6 except if they embed network addresses.

Major Features and Benefits of IPv6

The major specifications of IPv6 can be found at the IETF IPv6 working group and include:

IPv6 Header Improvements:
The IPv6 header format has been simplified for faster processing. It has a fixed size of 40 bytes and each field is 64-bits taking, therefore, an advantage of the current generation of 64-bits processors. Support for encoding options has been improved by daisy-chaining an extension to the header.

IPv6 Addressing:
As described in detail earlier, IPv6 introduces 128-bits addresses; half of the bits are used to identify the network and the other half to identify the host interface. Addresses are written as eight 16-bit integers. Each integer is represented by four hexadecimal digits as in:


IPv6 introduces a new type of address: anycast address which gives an address to a group of hosts but for which data is sent to only one of them. Broadcast addresses are replaced by multicast addresses and a single host interface can be assigned multiple addresses of any type (unicast, multicast, anycast). Addresses can be manually configured, assigned via DHCP or auto-configured/auto-generated.

IPv6 Auto-Configuration of Addresses:
IPv6 enables devices to have their addresses auto
configured. Hosts can get their network identification auto-configured, or expanded from a 48-bit MAC address (e.g., Ethernet address) auto-generated pseudo-random number. This auto-configuration enables “plug-and-play” deployment in particular of new consumer devices such as cell phones and home appliances and do not require any manual configuration or DHCP server.

Mobile IPv6:
With mobile IPv6, even though the mobile node changes locations and addresses, the existing connections through which the mobile node is communicating are maintained. To accomplish this, connections to mobile nodes are made with a specific address that is always assigned to the mobile node, and through which it is always reachable. Mobile IPv6 provides transport layer survivability when a node moves from one link to another by performing address maintenance for mobile nodes at the Internet layer.

IPv6 Routing Efficiency:
Like CIDR, the larger IPv6 address space enables the use of multiple levels of hierarchy inside the address space. Each level helps to aggregate the traffic at that level. So large address blocks are allocated to ISPs so that they can aggregate the prefixes of all their customers into a single prefix and announce that one prefix to the IPv6 Internet. Similarly, an enterprise network can use only one prefix for the entire network of the organization.

IPv6 QoS:
QoS in IPv6 is handled in the same way it is currently handled in IPv4 through the Traffic Class field implementing the DiffServ model. But IPv6 header has a new field named Flow label which can contain a label identifying a specific flow such as video stream or videoconference. The source node generates this flow label for the QoS devices in the path to take appropriate actions based on this label.

IPv6 Security:
While the use of IPSec is optional in IPv4, IPSec is mandatory in IPv6 and is part of the IPv6 protocol suite. Network implementers can enable IPSec in every IPv6 node and to provide authentication of the node, data integrity and data privacy.

Transitioning from IPv4 to IPv6

Before a transition to an end-to-end native IPv6 network, both service providers and enterprises have a number of migration paths from IPv4 to IPv6 in particular dual IPv4/IPv6 stack, IPv4 tunnels for IPv6 traffic and IPv6 NAT PT (protocol translation). The key is to deploy IPv6 at the edge where the applications and the hosts reside and then toward the core where the cost of moving to IPv6 is higher and the network operations are more challenging.

IPv4/IPv6 Dual stack backbone:
A core router supporting dual stack can forward packets to IPv4 and IPv6 nodes or to dual-stack nodes.  A host supporting dual stack can have applications that are not upgraded to run with IPv6 to coexist with IPv6 enabled applications.

IPv6 over IPv4 Tunnels:
IPv4 tunnels encapsulate IPv6 packets to connect isolated IPv6 sites or remote IPv6 networks over an IPv4 backbone.

IPv6 NAT PT provides bi-directional connectivity between IPv4 and IPv6 domains. A dual-stack router with interfaces in both IPv4 and IPv6 networks is capable of performing this function. The difference between IPv6 NAT PT and classic IPv4 NAT is that translations should be done both ways. Packets routed towards IPv4 hosts should have their source/destination addresses changed to IPv4 address equivalents and vice versa.

Note: The picture above is a sculpture from Auguste Rodin “Le Baiser”.

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Categories: Networking