[Dnsmasq-discuss] [PATCH] RADV: Send same RDNSS address as in DHCPv6

[Pali Rohár]

On Wednesday 20 January 2016 21:03:50 Simon Kelley wrote:
> On 16/01/16 15:10, Pali Rohár wrote:
> > On Friday 15 January 2016 22:37:46 you wrote:
> >> On 01/01/16 21:07, Pali Rohár wrote:
> >>> On Friday 01 January 2016 20:58:42 Simon Kelley wrote:
> >>>> Does the existing behaviour cause you problems? The rationale
> >>>> for why it behaves the way it does is that link-local
> >>>> addresses are good IF client and server are on the same link,
> >>>> since there's no possibility of addresses changing or
> >>>> renumbering. A client getting DNS server addresses from RADV
> >>>> is by definition on the same link as the server. One getting
> >>>> DNS addresses by DHCP is not (there may be a DHCP relay
> >>>> involved) but has DHCP to handle renumbering.
> >>> 
> >>> Hi! Reason is to provide same data over DHCPv6 and over RA.
> >>> This is
> >>> 
> >>> really useful to have consistency of connection data in whole
> >>> 
> >>> network.
> >>> 
> >>> When different addresses are sent over DHCPv6 and RA, correct
> >>> client behaviour is to use both (different) addresses in DNS
> >>> configuration.
> >>> 
> >>> But when I'm running one SW which doing everything needed for
> >>> IPv6
> >>> 
> >>> client subnetwork configuration I would expect that this SW
> >>> 
> >>> provide same data over all channels. Currently redundant
> >>> information over DHCPv6 and RA is only DNS (for now).
> >> 
> >> You can certainly configure it to do that, the default does
> >> different things for RA and DHCPv6 for the reasons I gave. Have
> >> you seen problems with those values when using RA and DHCP?
> > 
> > Problems? Not something which break functionality. Just that OS
> > adds two addresses (one l-l from RA and one from DHCPv6) to
> > /etc/resolv.conf and both addresses represent just one recursive
> > DNS (that where is running dnsmasq). Which I basically do not like
> > as there is only one recursive/forwarder DNS server.
> > 
> > Plus also that inconsistency on network that one configuration part
> > of IPv6 addresses (RA) send different information as another
> > configuration part (DHCPv6).
> > 
> >> If so, that's a bug, that needs to be fixed,  but otherwise, the
> >> best solution for you may be to configure dnsmasq rather than
> >> patching it.
> > 
> > Ok, configuration option for behaviour which I want is also OK. But
> > I dot want to hardcode full IPv6 address of machine where is
> > running dnsmasq as this address can be changed in time (because it
> > comes from DHCPv6 prefix delegation). Option --dhcp-range has
> > already fix for it, it accept address suffix with
> > constructor:<iface>.
> > 
> > But for specifying RDNSS option in dnsmasq it is not possible to
> > set global IPv6 address which comes from interface...
> 
> If you set the RDNSS address to be [::] then dnsmasq should
> substitute a global address of the interface, for both DHCPv6 and
> RA.

Great, it is working!

dhcp-option=option6:dns-server,[::]

-- 
Pali Rohár
pali.rohar at gmail.com
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