IPv4 Embedded IPv6 Unicast

[Benedikt Stockebrand]

Hello everybody,

Gergely Antal <skoal at skoal.name> writes:

> On Sat, 02 Jan 2010 18:13:47 +0000
> Nick Hilliard <nick-lists at netability.ie> wrote:
>
>> On 02/01/2010 17:47, The Dark One wrote:
>> > Experts,
>> > Junos accepts the following notation, very handy sometimes; do you
>> > know the exact official name for this kind of notation:
>> [...]
>> >         address 2001:1111:2222:3333::10.10.20.34/64;
>> 
>> "legacy view"?  "messed up mode"?
>> "let's-pretend-we're-still-using-ipv4 notation"? :-)
>> 
>> See RFC 2373, section 2.2 (Text Representation of Addresses) for more
>> information.  There appears not to be an official name for this
>> textual representation.

The term I have most commonly heard is "mixed notation".  But as far
as I know, you are right there is no official name for it.

All applications should support this as long as they use the standard
address parsing library functions (getaddrinfo(3) and the like), so it
isn't much a surprise that JunOS handles it correctly.

> Isn't this called v4inv6 ? 

No.  The notation is primarily intended for the the "IPv6-compatible
IPv4 addresses" (::/96) used with the deprecated (as of RFC 4213)
"automatic 6in4 tunnels" (RFC 2893) and for the "IPv4-mapped IPv6
addresses" (::ffff:0:0/96, RFC 3493) that IPv4 traffic is mapped into
before it is passed to an IPv6-oriented application.

As far as I know "v4inv6" isn't considered standard terminology; there
are "4in6" (short for "IPv4-in-IPv6") tunnels but they don't use any
kind of computed address mapping.

What's slightly annoying about the mixed notation is that it *doesn't*
work the middle of an IPv6 address: "2002:192.0.2.41:4711::/64" would
be handy with 6to4 tunnels.


Cheers,

    Benedikt

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