netdev - Re: ipv6_route flags RTF_ADDRCONF and RTF_PREFIX_RT are not cleared when static on-link routes are added during IPv6 address configuration

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Message-ID: <768cbcab-a172-4fe8-9c08-6550f5e12420@suse.de>
Date: Mon, 10 Nov 2025 17:54:39 +0100
From: Fernando Fernandez Mancera <fmancera@...e.de>
To: Garri Djavadyan <g.djavadyan@...il.com>, netdev@...r.kernel.org
Cc: Stephen Hemminger <stephen@...workplumber.org>, 1117959@...s.debian.org,
 carnil@...ian.org
Subject: Re: ipv6_route flags RTF_ADDRCONF and RTF_PREFIX_RT are not cleared
 when static on-link routes are added during IPv6 address configuration



On 10/25/25 11:21 PM, Garri Djavadyan wrote:
> On Sat, 2025-10-25 at 16:53 +0200, Salvatore Bonaccorso wrote:
>> Hi Garri,
>>
>> On Sat, Oct 18, 2025 at 01:39:02AM -0700, Stephen Hemminger wrote:
>>> On Thu, 16 Oct 2025 00:12:40 +0200
>>> Garri Djavadyan <g.djavadyan@...il.com> wrote:
>>>
>>>> Hi Everyone,
>>>>
>>>> A year ago I noticed a problem with handling ipv6_route flags
>>>> that in
>>>> some scenarios can lead to reachability issues. It was reported
>>>> here:
>>>>
>>>> https://bugzilla.kernel.org/show_bug.cgi?id=219205
>>>>
>>>>
>>>> Also it was recently reported in the Debian tracker after
>>>> checking if
>>>> the latest Debian stable is still affected:
>>>>
>>>> https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1117959
>>>>
>>>>
>>>> Unfortunately, the Debian team cannot act on the report because
>>>> no one
>>>> from the upstream kernel team has confirmed if the report in the
>>>> upstream tracker is valid or not. Therefore, I am checking if
>>>> anyone
>>>> can help confirm if the observed behavior is indeed a bug.
>>>>
>>>> Many thanks in advance!
>>>>
>>>> Regards,
>>>> Garri
>>>>
>>>
>>> Linux networking does not actively use kernel bugzilla.
>>> I forward the reports to the mailing list, that is all.
>>> After than sometimes developers go back and update bugzilla
>>> but it is not required or expected.
>>
>> Garri, best action would likely be to really post your full report on
>> netdev directly.
>>
>> Regards,
>> Salvatore
> 
> 
> Thank you for your suggestions Stephen and Salvatore.
> 
> Below is the full report that was originally posted to the kernel
> bugzilla a year ago. It is still reproducible with fresher kernels.
> 
> -----BEGIN REPORT-----
> I noticed that the ipv6_route flags RTF_ADDRCONF and RTF_PREFIX_RT are
> not cleared when static on-link routes are added during IPv6 address
> configuration, and it leads to situations when the kernel updates the
> static on-link routes with expiration time.
> 

This is indeed a bug, I have a patch already and I am doing some testing 
before sending it to net.git. I hope it can be sent tomorrow.

Thanks,
Fernando.