Re: question on RDNSS, RFC 6106 part 5.1

Ole Trøan <otroan@employees.org> Thu, 26 April 2012 12:00 UTC

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Sender: Ole Troan <ichiroumakino@gmail.com>
Subject: Re: question on RDNSS, RFC 6106 part 5.1
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Date: Thu, 26 Apr 2012 14:00:33 +0200
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Pavel,

I concur with your description of the problem.
do you have a proposal for how it can be solved?

Best regards,
Ole


On Apr 19, 2012, at 23:32 , Pavel Šimerda wrote:

> 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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