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

[Simon Kelley]

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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.


Cheers,

Simon.

> 

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