Re: question on RDNSS, RFC 6106 part 5.1

> Hello,
>
> I'm starting my work on linux NetworkManager. I've been following
> several bugreports during the recent months that all lead to problems
> with maintaining the list of recursive nameservers.
>
> I've already spent quite some time analyzing RDNSS problems and I came
> to a conclusion that the problem actually lives in the RFC itself.
>
> Please look at section 5.1. in RFC 6106. It states:
>
> MaxRtrAdvInterval <= Lifetime <= 2*MaxRtrAdvInterval
>
> Considering MaxRtrAdvInterval the maximum time between RAs, setting
> Lifetime to MaxRtrAdvInterval IMO constitutes a race condition.
> Moreover, any Lifetime in this interval can timeout with just one or two
> lost RAs.
>
> This makes RA-based IPv6-only networks drop RDNSS regularly. In many
> implementations IPv6 and IPv4 are bound together so that if one of them
> fails, the whole link is restarted. This is also the case in
> NetworkManager.
>
> In the current situation, it's not advisable to use RFC 6106 in
> production because it can cause problems even to IPv4 applications.
>
> In the real world, radvd uses Lifetime=MaxRtrAdvInterval by default and
> NetworkManager internally adds 10s to the lifetime, that only helps to
> avoid the race condition but not lost packets that are common on
> wireless networks.
>
> I appreciate any help to get this right both in the standards and in the
> software.
>
> Cheers,
>
> Pavel Šimerda
>
>
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