[Mono-bugs] [Bug 668998] New: IPAddress ToString() uses mixed notation for IPv6 loopback address

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https://bugzilla.novell.com/show_bug.cgi?id=668998

https://bugzilla.novell.com/show_bug.cgi?id=668998#c0


           Summary: IPAddress ToString() uses mixed notation for IPv6
                    loopback address
    Classification: Mono
           Product: Mono: Class Libraries
           Version: 2.6.x
          Platform: Other
        OS/Version: Other
            Status: NEW
          Severity: Normal
          Priority: P5 - None
         Component: System
        AssignedTo: mono-bugs at lists.ximian.com
        ReportedBy: oskar.berggren at gmail.com
         QAContact: mono-bugs at lists.ximian.com
          Found By: ---
           Blocker: ---


User-Agent:       Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.2.13)
Gecko/20101206 Ubuntu/10.04 (lucid) Firefox/3.6.13

IPAddress.Parse("::1").ToString() results in "::0.0.0.1", i.e. mixed notation. 

This happens for all IPv6 addresses that begin with 96 zero bits, including the
IPv6 loopback address, which is surprising and feels... wrong. Furthermore,
this differs from the .Net output, where "::1" is used.

IPv6 addresses that begin with 96 zero bits were defined as IPv4-compatible
addresses. These were deprecated by RFC4291, section 2.5.5.1 in 2006, as also
noted on IANA
(http://www.iana.org/assignments/ipv6-address-space/ipv6-address-space.xml).

Some further experiments on the .Net implementation:
For an IPv6 address ::x:y, the MS notation seems to use mixed-notation whenever
x is non-zero. Otherwise regular IPv6-notation is used, which makes the IPv6
loopback actually look like an IPv6 address.

The Mono behavior should be changed to match MS on this. Or at least use
regular IPv6 notation for the loopback address.

Reproducible: Always

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