Re: [Bugme-new] [Bug 15720] New: IPv6's ipv4-compatibility addresses don't bind

Re: [Bugme-new] [Bug 15720] New: IPv6's ipv4-compatibility addresses don't bind

[Andrew Morton]

(switched to email.  Please respond via emailed reply-to-all, not via the
bugzilla web interface).

On Wed, 7 Apr 2010 23:17:32 GMT bugzilla-daemon@bugzilla.kernel.org wrote:

> https://bugzilla.kernel.org/show_bug.cgi?id=15720
> 
>            Summary: IPv6's ipv4-compatibility addresses don't bind

A 2.6.9 -> 2.6.32 regression ;)

>            Product: Networking
>            Version: 2.5
>     Kernel Version: 2.6.32-2-686-bigmem
>           Platform: All
>         OS/Version: Linux
>               Tree: Mainline
>             Status: NEW
>           Severity: normal
>           Priority: P1
>          Component: IPV6
>         AssignedTo: yoshfuji@linux-ipv6.org
>         ReportedBy: charles@kde.org
>         Regression: Yes
> 
> 
> When attempting to bind to an address using ipv4-compatibility, for example,
> "::ffff:127.0.0.1", Linux refuses to bind to that address when
> /proc/sys/net/ipv6/bindv6only is set.
> 
> Yes, you could say "but you specifically told ipv6 to not bind to ipv4
> addresses!" However, ::ffff:127.0.0.1 is *clearly* an ipv4 address, it's not an
> alternate representation of an ipv6 address, it's an ipv4 address and only
> ipv4.
> 
> This seems to not have been the case as of linux 2.6.9, although I'm not sure
> at what version this changed.
> 
> It seems to me that the intent of "bindv6only" was to not bind to the ipv4
> address when you bind to all addresses (specifically ipv6 address "::"). So
> when you bind to ::, an ipv4 client connects to you, and it appears to be
> connecting from ::ffff:192.168.5.5. I don't think its intent was to effectively
> disable binding to ::ffff:x.x.x.x addresses - just breaking that feature makes
> no sense.
> 
> The Linux 2.6.9 approach seems to match MacOS's (and I'm pretty sure Solaris's,
> too).

Re: [Bugme-new] [Bug 15720] New: IPv6's ipv4-compatibility addresses don't bind

[Brian Haley]

Andrew Morton wrote:
>> When attempting to bind to an address using ipv4-compatibility, for example,
>> "::ffff:127.0.0.1", Linux refuses to bind to that address when
>> /proc/sys/net/ipv6/bindv6only is set.

This is actually not a (deprecated) IPv4-compatible IPv6 address (::127.0.0.1),
but an IPv4-mapped IPv6 address.

>> It seems to me that the intent of "bindv6only" was to not bind to the ipv4
>> address when you bind to all addresses (specifically ipv6 address "::"). So
>> when you bind to ::, an ipv4 client connects to you, and it appears to be
>> connecting from ::ffff:192.168.5.5. I don't think its intent was to effectively
>> disable binding to ::ffff:x.x.x.x addresses - just breaking that feature makes
>> no sense.

It is documented in ip-sysctl.txt:

bindv6only - BOOLEAN
        Default value for IPV6_V6ONLY socket option,
        which restricts use of the IPv6 socket to IPv6 communication
        only.
                TRUE: disable IPv4-mapped address feature
                FALSE: enable IPv4-mapped address feature

        Default: FALSE (as specified in RFC2553bis)

-Brian