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Putting IPv6 Addresses into Context

Because IPv6 is so much larger than IPv4, the IETF has been able to structure the address space more neatly.  Page 1Consequently, it is easier to distinguish between different address types based on the first few characters in the address, rather than having to refer to registry, as is often the case with IPv4.

Nonetheless, there are a lot of addresses and lots of new things to learn if you are only familiar with an IPv4 environment. But as we implement IPv6 across our networks we will see IPv6 addresses popping up in mail headers, system logs, traceroutes and all sorts of other places where IPv4 used to be used exclusively. Knowing quickly whether an address is part of your own network or someone else’s; whether an address is intended for private use or Internet use; and knowing whether an address is used by a transition mechanism or a native connection will help save lots of time.

Last year, ICANN staff worked with the staff at APNIC and the RIPE NCC to produce a single sheet that identified the key address groups, explained what they were and gave IPv4 examples of IPv4 equivalents where they existed. This year we have updated the sheet and you can grab a copy of the updated reference from here.

This reference will be useful for anyone working on an abuse desk, in a Network Operations Centre or a corporate IT department. Even if you don’t plan to roll out IPv6 on your own network in the next few months, you are likely to see it appearing on other networks. Using our cheat sheet can help bring you up to speed quickly and identify where to look for an address faster than by just consulting the on-line registries.

Page 2We want this reference guide to be as useful and current as possible, so as things change in the future we will produce further updates for you to use.


    Domain Name System
    Internationalized Domain Name ,IDN,"IDNs are domain names that include characters used in the local representation of languages that are not written with the twenty-six letters of the basic Latin alphabet ""a-z"". An IDN can contain Latin letters with diacritical marks, as required by many European languages, or may consist of characters from non-Latin scripts such as Arabic or Chinese. Many languages also use other types of digits than the European ""0-9"". The basic Latin alphabet together with the European-Arabic digits are, for the purpose of domain names, termed ""ASCII characters"" (ASCII = American Standard Code for Information Interchange). These are also included in the broader range of ""Unicode characters"" that provides the basis for IDNs. The ""hostname rule"" requires that all domain names of the type under consideration here are stored in the DNS using only the ASCII characters listed above, with the one further addition of the hyphen ""-"". The Unicode form of an IDN therefore requires special encoding before it is entered into the DNS. The following terminology is used when distinguishing between these forms: A domain name consists of a series of ""labels"" (separated by ""dots""). The ASCII form of an IDN label is termed an ""A-label"". All operations defined in the DNS protocol use A-labels exclusively. The Unicode form, which a user expects to be displayed, is termed a ""U-label"". The difference may be illustrated with the Hindi word for ""test"" — परीका — appearing here as a U-label would (in the Devanagari script). A special form of ""ASCII compatible encoding"" (abbreviated ACE) is applied to this to produce the corresponding A-label: xn--11b5bs1di. A domain name that only includes ASCII letters, digits, and hyphens is termed an ""LDH label"". Although the definitions of A-labels and LDH-labels overlap, a name consisting exclusively of LDH labels, such as"""" is not an IDN."