[Dnsmasq-discuss] dnsmasq and external DHCPv6 servers

[Eric Dittman]

On 1/5/22 4:57 PM, Simon Kelley wrote:
> On 03/01/2022 21:55, Eric Dittman via Dnsmasq-discuss wrote:
>> I have a Ubiquiti UDM SE.  It uses dnsmasq for DNS, DHCP, and RAs.  I
>> have external DNS and DHCP servers so I want to send RA packets with
>> the M and O flags set and the A flag reset, but I can't figure out the
>> proper configuration to do that.  Right now just to get RA working on
>> the subnets for IPv6 I have the following:
>>
>> enable-ra
>> ra-param=*,high,0
>> domain=mydomain
>> dhcp-range=2001:470:xxxx::,ra-names,slaac
>> dhcp-range=2001:470:xxxx:10::,ra-names,slaac
>> dhcp-range=2001:470:xxxx:20::,ra-names,slaac
>> dhcp-range=2001:470:xxxx:40::,ra-names,slaac
>>
>> I'm getting autoconf IPv6 addresses but I'm not seeing any DHCPv6
>> packets on the external DHCPv6 servers (a pair per subnet).
>>
>> Any ideas how I can get this working?
> 
> The dnsmasq RA code was designed to work with the dnsmasq DHCPv6 server,
> so there's no direct support for this. I think the closest you can get
> is to configure a static-addresses-only dhcp range
> 
> dhcp-range=2001:470:xxxx:10::,static,slaac
> 
> Which will not allocate any DHCPv6 leases, leaving the field open for
> you other DHCPv6 servers, but will set the M and O bits.
> 
> Adding a new keyword to cover this circumstance is pretty straightforward.

Thanks, Simon, that worked!  I really appreciate it.

The only issue I'm having now is I'm getting the router link-local IPv6
address included along with the two IPv6 addresses I specify in the
DHCPv6 options for the DNS resolvers:

nameserver 2001:470:xxxx:10::105
nameserver 2001:470:xxxx:10::106
nameserver fe80::300d:e6ff:fe85:e6e0
nameserver 10.0.10.105
nameserver 10.0.10.106
-- 
Eric Dittman