[Dnsmasq-discuss] update on dnsmasq and IPV6 networks

[Simon Kelley]

On 16/09/12 20:05, Gene Czarcinski wrote:
> As stated in other email, I am interested in using dnsmasq to support
> dhcp and even more important dns services on an IPv6 network. To support
> this, I am doing a bunch of testing using qemu/kvm/libvirt
> virtualization with three virtual guests and two virtual networks defined.
>
> The first network is a regular "nat" network connected to the outside
> world and only guest1 is connected to it. The second network is a
> "private" network [no forwarding], has both IPv4 and IPv6 networks
> defined, and is connected to all three guests.
>
> I am running this on Fedora 17 and using NetworkManager which certainly
> adds some complexity.
>
> The two testing guests (guest2 and guest3) depend on guest1 for dhcp (or
> ra) and dns services.
>
> Guest1 is running dnsmasq configured to support both IPv4 and IPv6 with
> dhcp and dns services. The dhcp6 parameters are changed to test
> different tests/configurations. Although there are a number of different
> ways of configuring dnsmasq, I am interested in primarily two: ra-names
> and no mode specified which appears to mean that dnsmasq should act as a
> real dhcp6 server.
>
> 1. ra-names ... it works. Guest2/guest3 initialize IPv4 with dhcp and
> use something (slaac I believe) to get an IPv6 address [NetworkManage
> "automatic" mode for IPv6]. Then dnsmasq goes through its dance to to
> add the IPv6 address under the FQDN of the same system with the IPv4
> address. Note: for IPv4 dhcp, NetworkManager does a "send host-name" so
> that dnsmasq has something to work with.
>
> 2. dhcp6 ... The dnsmasq configuration is set with no "enable-ra" and no
> mode specified on the dhcp-range specification (just IPv6 start/end
> addresses and a prefix). Does not work ... well, it sort of does ... the
> IPv6 address as defined to dnsmasq is assigned to the guest (which is in
> NetworkManager IPv6 dhcp only mode). However, the dns is not updated.
> Running wireshark on guest1, I do not see guest2/guest3 supplying any
> names in their DHCPV6 chatter.
>
> I did some testing and proved (to my satisfaction) that the reason
> dnsmasq does not update the dns is that NetworkManager is not send the
> info. I stopped NetworkManager, changed the ifup-eth network script
> slightly [for dhclient -6 change the "-H" to "-F"] and did a "ifup
> eth0". Wireshark now showed the system sending fqdn.fqdn info and is I
> did host I got both IPv4 and IPv6 address for the system.
>
> Looking at the lease file I see:
> -----------------
> lease6 {
> interface "eth0";
> ia-na 00:d1:4f:88 {
> starts 1347810642;
> renew 1800;
> rebind 3150;
> iaaddr fd00:dead:beef:4::14e {
> starts 1347810642;
> preferred-life 3600;
> max-life 3600;
> }
> option dhcp6.status-code success "Oh hai from dnsmasq";
> }
> option fqdn.encoded true;
> option fqdn.server-update true;
> option fqdn.no-client-update true;
> option fqdn.fqdn "test4.privnet6";
> option fqdn.hostname "test4";
> option fqdn.domainname ".privnet6";
> option dhcp6.client-id 0:1:0:1:17:e8:b1:d1:52:54:0:d1:4f:88;
> option dhcp6.server-id 0:1:0:1:17:e5:df:c2:52:54:0:6c:9a:51;
> option dhcp6.name-servers fe00:dead:beef:4::91;
> }
> -----------------
>
> According the the dhcp-options man-page, the fqdn.fqdn (at least for
> IPv6) can be specified as eather a plain name to be filled out by the
> dhcp server or a real fully qualified domain name wit the string ending
> in a period ".". The way I had "dhclient -6" sending a plain name with
> the "-F".
>

I've just read through this thread and it looks like you've got to the 
truth for what needs to provided. Good. Sorry I missed out on helping 
earlier.

> Now the really interesting thing is that once I had sent the fqdn info
> is that this system continued to have the dhcp6 address and an IPv6
> entry in the dns. I deleted the leases on the client and restarted
> dnsmasq but it continues.

The name will continue to be associated with the lease by dnsmasq until 
the lease expires or the client releases it.

Simon.