[Dnsmasq-discuss] [PATCH] DHCPv6 - Multiple reservations for single host

Oliver Freyermuth o.freyermuth at googlemail.com
Mon Jan 27 12:25:52 GMT 2020

Dear Harald,

Am 27.01.20 um 10:05 schrieb Harald Jensås:
> On Sun, 2020-01-26 at 20:01 +0100, Oliver Freyermuth wrote:
>> I also like this new approach. "Wasting" 4 addresses for one host
>> seems to be the only way
>> to solve this while conforming to RFCs. 
>> However, there's one issue I can't find a good solution for in this
>> scheme - 
>> how to solve the "DNS problem" if dnsmasq is only used for DHCP, but
>> DNS is provided by other means? 
>> The "range reservation", as highlighted, means the final address is
>> not well predictable (may depend on hardware,
>> other parts of the boot process etc.). 
>> When dnsmasq is also doing the DNS part, that's not a problem, since
>> it will use the final / "most recently leased" address for DNS. 
>> Does anybody have a good proposal for the case when DHCP is provided
>> by dnsmasq but DNS is maintained separately
>> (i.e. the "final address" needs to be fixed)? 
>> Cheers,
>>         Oliver
> I think adding tag support for dhcp-host entries as follow up.
> The idea would be to have a config like this:
> dhcp-match=set:efi6,option6:61,0007 
> dhcp-match=set:efi6,option6:61,0009
> dhcp-match=set:efi6,option6:61,0011
> # User class is iPXE
> dhcp-userclass=set:ipxe6,iPXE
> dhcp-host=tag:efi6,tag:ipxe6,52:54:00:bc:c3:fd,[fd12:3456:789a:1::bb00/126],host2
> dhcp-host=tag:!efi6,tag:!ipxe6,52:54:00:bc:c3:fd,[fd12:3456:789a:1::bb05],host2
> The "temporary addresses" in [fd12:3456:789a:1::bb00/126] are only used
> when architecture type is one of the UEFI types or the userclass option
> have "iPXE". The dhcp client in the final OS should always end up with
> fd12:3456:789a:1::bb05.

nice! Really helpful, that looks like it should work - I was just not clever enough to come up with that :-). 
Our setup is sadly a bit clumsy - we have "Web-GUI-access" (no API :-( ) to one central DHCP/DNS appliance which can do DNS for v4/v6 and DHCPv4, but not DHCPv6 (due to other network components in between). 
So while we want to keep the information and DNS at that one central place, we have to use dnsmasq for DHCPv6 for now and manually sync information. 

Using the tag-based approach, this should work fine. We'll likely get to test this at larger scale in the upcoming months,
and I may be able to do a test at small scale in the next weeks based on your patch (need to find a time-slot first...). 

Cheers and thanks,

> Another possible solution would be to use a dhcp-script which run's
> nsupdate to dynamically update the dns server.
> --
> Harald

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