[Dnsmasq-discuss] local.net / ipv6 confusion

Simon Kelley simon at thekelleys.org.uk
Thu Oct 24 13:57:36 BST 2013

On 22/10/13 19:39, Ken Bass wrote:
> Hello,
> My dnsmasq.conf file contains (running on my asus (merlin) router -
> using dnsmasq 2.65):
> domain=local.net
> local=/local.net/
> and
> dhcp-option=lan,option:domain-search,local.net
> Everything was working fine. I use server1.local.net as a FQDN
> throughout my local network.
> And then yesterday I enabled ipv6 on my router and this all stopped
> working (or maybe only on windows machines). So I am wondering if I
> could get some help on how to fix this.
> My suspicion is that the resolver on Windows machines is perhaps
> ignoring my local DNS server and instead querying an actual ipv6 server
> from the ISP so it never finds my host.local.net names.
> I did verify via some test websites that the router is working with
> native ipv6.
> The router is currently running radvd, dhcp6c, and dhcp6s.
> So i think the solution to this is for dnsmasq to at least handle dns
> queries locally and forward them.
> 1) Do I need radvd or is 'enable-ra' equivalent? I noticed in my
> /etc/radvd.conf file that 'AdvLinkMTU 1480'. I dont see how dnsmasq does
> an equivalent thing and whether this is even important.
> 2) I've changed the RDNS in the /etc/radvd.conf and replaced it with the
> ipv6 of my router.
> 3) On windows 7, is there something I need to do to force a refresh of
> these ipv6 dns servers? They don't seem to change even with ipconfig
> /release and /renew. However after rebooting my router and waiting 10-15
> minutes, it seemed to update.
> 4) I am thinking that for dnsmasq to handle the ipv6 queries, it needs
> to bind on the ipv6 address and that can only occur if I add a
> dhcp-range (which means killing dhcp6s)?
> I added the following
> dhcp-range=lan6,XXXX:XXXX:XXXX:XXXX::, ra-stateless, ra-names
> dhcp-option=lan6,option:domain-search,local.net
> #ISP ipv6 DNS
> server=2001:558:feed::1
> server=2001:558:feed::2
> Am I on the right track? Currently it seems to work (still using radvd),
> though I'm not sure if it is my imagination, but latency to websites
> seem longer. Are added DNS lookups causing this?
> This appears to be working which raises other questions (perhaps more
> ipv6 related).
> - When I look some of my existing Linux machine with ifconfig, I notice
> that they have an ipv6 global address which contains the correct prefix.
> Where did this come from? I am unaware that those machine are running
> any dhcpv6 client. I did nothing to them, yet they can ping6 the router
> and ipv6.google.com. Does the ip stack handle processing router
> advertisements itself? How does it know?

Indeed, the kernel handles router advertisements.

> - How do I assign meaningful ipv6 DNS names to these when they are using
> this stateless configuration? Or do I need to use stateful?

You have two options. The obvious one is to use stateful DHCPv6. The 
other, if you're using DHCP for v4 is to use ra-names. Dnsmasq should be 
able to work out the stateless IPv6 address associated with a client and 
assign the same name as that client has for IPv4.

> - Now that I've got this wonderful /64 address space, if I want to
> access these machines from the internet do I need to do anything special?

You mean, to be able to look them up in the DNS anywhere? You have lots 
to do. See the AUTHORITATIVE CONFIGURATION section of the man page for a 



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