– By Jeff Doyle president of Jeff Doyle and Associates,
We are entering the transitional period between IPv4 andIPv6, and things are going to get awkward for a while. IPv4 addresses will officially be used up in the next couple of years, although for most practical purposes you can consider the pool of unallocated IPv4 addresses to be depleted already. I know of two very large service providers whose requests for new IPv4 allocations were, in the last couple of months, denied.
The “awkward period” we are entering is caused by several unavoidable facts:
1) With few exceptions, the only new globally unique unicast addresses you can get from your regional address registries are IPv6. Those organizations are becoming very protective of the few IPv4 blocks they have left, and even those will be gone in short order.
2) The vast majority of the user devices connecting to theInternet are IPv4.
3) The vast majority of content accessible over the Internet is IPv4 only.
4) The vast majority of service provider connectivity to their customers remains IPv4 only. Getting even basic connectivity to the “IPv6 Internet” usually requires some form of IPv6-over-IPv4 tunneling, and the average user has no motivation to enable this.
5) Although modern operating systems are fully IPv6 capable (Windows Vista, MAC OS, most flavors of Unix), there is still a huge installed base of operating systems that either have limited IPv6 support (Windows XP) or none at all.
6) Service providers are faced with growing their network using IPv6, while continuing to serve legacy IPv4 customers. They are going tobe coping with some unwieldy logical architectures for a while.
7) New customer networks will probably continue to spring up using private IPv4 addresses, even if all the gear they install is IPv6 capable. It will take years for IT personnel to become comfortable with IPv6.The difference is that increasingly, the public side of their NAT devices is going to be IPv6 rather than IPv4.
Coping with the early transitional years, in which most content and users are still on IPv4 but the only new addresses are IPv6, falls heavily on service providers. They cannot continue giving customers globally routable IPv4 addresses, they cannot get new globally routable IPv4 addresses for expanding their own networks, and yet they must continue to serve both legacy IPv4 customers and new customers – all of whom are primarily trying to reach IPv4 destinations.
Keep in mind that the vast majority of broadband customers could care less whether their application traffic is riding over IPv4 or IPv6, or even know what IP is. Customers care about services, and how well those services are delivered. So any effort by a service provider to introduce IPv6 that reduces service quality or inconveniences their customers is going to be costly. In an intensely competitive market, even perceptions matter: A customer might not have run Windows 95 for years, and his IPv4-only game system might be gathering dust in the closet, but tell him that he cannot use them and he might switch providers.
Therefore IPv4 and IPv6 must coexist for some number of years, and their coexistence must be transparent to end users. In fact if an IPv4-to-IPv6 transition is successful, the end users should not even notice it.
The tools available to networkers for IPv4/IPv6 coexistence fall into one of four categories:
· Dual stack: A dual stack device is “bilingual;” that is, it can originate and understand both IPv4 and IPv6 packets.
· Manually configured tunnels: A tunnel carries IPv4 packets in IPv6, or IPv6 packets in IPv4. A manually configured tunnel is one in which the network operator specifies the endpoints of the tunnel and the encapsulation technology; the tunnel stays up until the operator removes it. Manual tunnels are ideal for connecting IPv6 sites over IPv4 or vice versa. IP in IP, GRE, and MPLS are the usual technologies used.
· Automatic tunnels: 6to4, ISATAP, DSTM, and tunnel brokers are the most prominent examples of automatic tunnels; these technologies are best applied when temporary tunneling is required. Unlike manual tunnels, automatic tunnels identify their own endpoints and are set up and torn down as needed.
· Translators:These are used when an IPv4-only device must speak to an IPv6-only device, or when some portion of the network between two end systems can only carry one IP version. Some translators, such as NAT-PT, work at the network layer and convert all packets of one version to packets of the other version. Other translators are Application Layer Gateways (ALGs) that only convert packets belonging to certain applications.
Dual stacking is by far the preferable solution in most scenarios. The dual stacked device can speak equally to IPv4 devices, IPv6 devices, and other dual-stacked devices (with the two devices agreeing on which IP version to speak). And the entire transition can be driven by DNS: If a dual-stacked device queries the name of a destination and DNS gives it an IPv4 address (a DNS A Record), it sends IPv4 packets. If DNS responds with an IPv6 address (a DNS AAAA Record), it sends IPv6 packets.
Article Source: http://www.networkworld.com/community/node/42436
