[Dnsmasq-discuss] IPv6 and domain name with ntp-server option

[Yeoh]

> Hi Yeoh,
>
> On 28.07.24 23:42, Yeoh via Dnsmasq-discuss wrote:
>> Does 'option:42' or 'option:ntp-server' support using IPv6 addresses or a domain name ?
>>
>> I mean instead of using an IP literal address we can instead specify a domain name that resolves to multiple IP's (IPv4/IPv6).
>
>
> DHCP is strictly IPv4, and RFC 2132 defines option 42  as 'a list of IP
> addresses'.
> This would neither allow domains nor IPv6 addresses.
>
> For IPv6, DHCPv6 is the equivalent protocol.
>
> RFC 5908 allows to state an IPv6 address as well as a FQDN as a
> suboption of option code 56, where the NTP servers conveyed in either
> way should be part of the organisation that configures them (in an
> effort to reduce load on public NTP servers).
>
> dnsmasq supports IPv6 addresses notated as
> dhcp-option=option6:ntp-server,[1234::56].
> I am unaware whether FQDNs would be allowed as well. The documentation
> mentioning only IPv6 addresses seems to suggest they are currently not.
>
> However, note that IPv6 clients commonly would prefer SLAAC over
> stateful or stateless DHCPv6 to configure their network stack. There are
> even OSs that do not support DHCPv6 at all, Android being the prime
> example here.
>
> With NDP/SLAAC, clients should pick up network information from Router
> Advertisements as broadcasted by a router.
> I am not aware of an RFC defining router advertisements conveying NTP
> server information.
>
> Thus, using DHCP with IPv4 addresses would seem the most reliable way to
> convey NTP server information to IPv4 as well as dual stack clients.
>

Hi Buck,

Thanks for the hint. DHCPv6 option6 for ntp-server does indeed take an FQDN too.

Regards,
Yeoh