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In RFC 5952 - section 5 it is stated that for some IPv6 addresses it is recommended to give the mixed notation, if it has a certain prefix. However, it is unclear which prefixes are used for this, because it is stated that a prefix may be used if it is commonly used as a prefix for a IPv4-mapped address. Thus meaning basically any prefix could be used for this.

Now my question is:
May every IPv6 address be written as an IPv4-mapped IPv6-address?
If not, what are the exact rules for correctly writing an IPv4-mapped IPv6-address?

So can every IPv6 address be written in the format of:

x:x:x:x:x:x:d.d.d.d

Afterwards applying the compression for IPv6 text representation to the hexadecimal part.

  • Depending on the resolver, an address can be input in any (mixed) format the parser understands. All dot-decimal, to full 0xHEX. The convention is to use colon-notation for the IPv6 part and dot-decimal for the IPv4 part to indicate an IPv4 embedded address to human readers. (on the wire, an address is an address) – Ricky Beam Feb 3 '15 at 8:47
  • @RickyBeam I am aware of the fact that on the wire an IPv6 address is transferred as a 128-bits-long stream. However, I'm wondering when the IPv4 embedded IPv6 address should be used, and when a full hex-notation is preferred. There should be standards set for these writing styles - Unfortunately the RFCs are a bit unclear on this part. – Dennis Feb 3 '15 at 12:29
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    @Dennis - RFC 5952, A Recommendation for IPv6 Address Text Representation, Section 5, Text Representation of Special Addresses, addresses this: tools.ietf.org/html/rfc5952#section-5 – Ron Maupin Feb 3 '15 at 14:58
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The only IPv4-mapped IPv6 address that I have seen/know of is ::FFFF:/96.

Examples:

  1. The above is used for sharing IPv6 network prefixes over IPv4 transport in BGP:

http://www.juniper.net/documentation/en_US/junos13.2/topics/example/bgp-ipv6.html

  1. F5 LTM Appliance. Even if the user configures IPv4 addresses for the box, internally all addresses are treated/converted to IPv6.

https://devcentral.f5.com/articles/ipaddr-and-ipv6

Explanation for IPv4-mapped IPv6 addresses is available here:

http://www.tcpipguide.com/free/t_IPv6IPv4AddressEmbedding-2.htm

Hope this helps.

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