[Dnsmasq-discuss] dnsmasq 2.62-3 as DHCPv6-Server and RA-Server: Bug sending router's link-local instead of global address as gateway and DNS-server?

Simon Kelley simon at thekelleys.org.uk
Tue Jan 21 22:28:50 GMT 2014

On 21/01/14 13:02, Martin Babutzka wrote:
> Thanks for the replies! I hesitantly updated to dnsmasq-2.68 since I
> first wanted to stick to the version provided with Debian wheezy. The
> quiet-options really reduce the amount of syslog messages except for:
> "dnsmasq-dhcp[23663]: no address range available for DHCPv6 request via
> eth5"
> Concerning the link-local addresses it actually looks like this is the
> default when advertising gateways in local networks. Unfortunately other
> software to proxy/relay dhcpv6 and ra can not handle it properly. It is
> basically possible to also advertise the routers global address (see
> here: http://www.macfreek.nl/memory/Non-Local_IPv6_Router_Advertisement
> and the RFC here: http://tools.ietf.org/html/rfc6275#section-7.2 ). Is
> this option also available in dnsmasq? In radvd it is called
> "AdvRouterAddr on;".

There are two different thinks here: the router address and the DNS 
server address.

I think that the router address is always taken as the source address of 
the RA packets, and therefore has to be link-local.

The DNS server address is advertised as the global address in DHCPv6 and 
the link-local address in RA, by default.

You can force a particular address in RA and DHCpv6 by using 
dhcp-option, indeed you can specify the option is all zeros to specify 
the global address. This applies to both DHCPv6 and RA so


will force the dhcpv6 DNS address to be the global address (no change) 
and the RA DNS address to be the same, which is what you want, I think.

The next release adds the ability to specify link-local, ULA or global 



> Many regards,
> Martin
>> Kevin Darbyshire-Bryant <kevin at darbyshire-bryant.me.uk> hat am 21.
>> Januar 2014 um 12:16 geschrieben:
>> On 21/01/2014 10:40, Martin Babutzka wrote:
>>> Hello,
>>> We are using this great piece of software so far as DNS cacher but
>>> want to implement it also as IPv6 server by now. DHCPv4 is handled by
>>> another software at the moment (isc-dhcp-server) but we think the
>>> dnsmasq 2.62-3 is quite suitable for our need of an DHCPv6- and
>>> RA-server.
>>> I activated the features in dnsmasq.conf which I think should set-up
>>> a working DHCPv6/RA-Server (see compressed config file below). From
>>> then on the server distributed ipv6-addresses from the correct range.
>>> Unfortunately some error occured: As wanted it also distributed
>>> Gateway and DNS-server but it used the LINK-LOCAL v6 address of the
>>> corresponding interface instead of the Global configured address
>>> (2010:7d0:904:1202::1). Is this a bug or misconfiguration?
>>> Another independent question: With this configuration dnsmasq starts
>>> to be pretty noisy in the syslog. Is there any option to reduce the
>>> verbosity once the system works?
>> v2.68 includes 'quiet-dhcp, quiet-dhcp6 & quiet-ra' options which
>> significantly help the syslog noise.
>> I think it's correct behaviour to advertise the link-local address.
>> Hope that helps.
>> Kevin
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