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

Pali Rohár pali.rohar at gmail.com
Sat Jan 16 15:10:07 GMT 2016


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...

-- 
Pali Rohár
pali.rohar at gmail.com
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