Hello, my proposition is the same as Teemu's or very similar.
1) I propose to change the default Lifetime from [MaxRtrAdvInterval, 2*MaxRtrAdvInterva] to a single agreed-upon recommended default value. Almost nobody would need to change this default value. 5*MaxRtrAdvInterval is IMO a good value to start with. This should be enough to avoid the need to send RS. 2) I propose to add at least some best practice about router solicitations. Typically, RS should only be used as a last resort. I suggest to start sending RS at 0.8*Lifetime +/- 0.1*Lifetime (if sending RS at all) and repeat let's say every 10-20 seconds. Note: Please remember that wireless links *sometimes* lose packets. Please remember that wireless links *often* lose multicast packets. Even some ethernet switches do. Example: MaxRtrAdvInterval = 10 minutes AdvRDNSSLifetime = (Default) 5*MaxRtrAdvInterval = 50 minutes 0.8*Lifetime = 40 minutes 0.1*Lifetime = 5 minutes Let's simplify the situation and act as if MaxRtrAdvInterval is the absolute interval (it is not!). 00:00 Router Advertisement, Lifetime = 50 minutes 00:10 Lifetime = 40 minutes (it could already time out according to the current RFC) 00:10 Router Advertisement (lost) 00:20 Lifetime = 30 minutes 00:20 Router Advertisement (lost again) 00:30 Lifetime = 20 minutes 00:30 Router Advertisement (lost the third time!) 00:35 Lifetime = 15 minutes 00:35 This is the first time RS can be sent with this best practice (the last time is 00:45, counted like that 0.8*00:50 +/- 0.1*00:50) 00:35 Router Solicitation Since then, router solicitations would be issued regularly until client recieves RA with RDNSS, connection is cancelled by user or: 00:50 Lifetime = 0 00:50 RDNSS expired Note: It is not perfect. The concept of finitely valid RDNSS is quite new. There is an open question, when to consider RDNSS information lost. It could be: 1) Last RDNSS from RAs expired. 2) Last IPv6 RDNSS expired (RDNSS or DHCPv6) 3) Last RDNSS lost (IPv6 or IPv4) Pavel Simerda On Thu, 2012-04-26 at 14:00 +0200, Ole Trøan wrote: > 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 > > > > > > -------------------------------------------------------------------- > > IETF IPv6 working group mailing list > > ipv6@ietf.org > > Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6 > > -------------------------------------------------------------------- > -------------------------------------------------------------------- IETF IPv6 working group mailing list ipv6@ietf.org Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6 --------------------------------------------------------------------
