[Dnsmasq-discuss] DHCPv6 with dnsmasq for automated deployments

[Roy Marples]

On 03/06/2018 22:20, Simon Kelley wrote:
> I agree that this is an annoying problem. In DHCPv6 even determining the
> MAC address of a client is a slightly dodgy operation - there are
> circumstances where it's not possible. That notwithstanding, dnsmasq
> does it's best, and allows you to configure an address to allocated by
> MAC address.
> 
> The problem here is that the client changes DUID - the desired address
> gets allocated by MAC address once, but when the DUID changes, the
> address is already in use by a first DUID/IAID combination, so it can't
> be allocated, even if the MAC address is the same.

The problem is how the DUID is generated, not the DUID itself.
DUID-LL is not the default (and shouldn't be either).
DUID-LLT is a good default, but comes with the aforementioned problems.

These problems are very nicely solved with RFC 6355 which adds DUID-UUID 
where UUID is taken from the hosts firmware. The UUID can then be 
displayed on the node alongside the MAC address for provisioning.
https://tools.ietf.org/html/rfc6355

The downside is that no client I know of supports this and I keep 
meaning to add support to dhcpcd for it.
The other downside is that not all hosts have a retrievable UUID as it 
depends on both the OS and host itself - for example some OS's present a 
UUID based on the CPUID. Of course this only works if all OS's generate 
the same UUID from the base data.

TL;DR - this isn't a dnsmasq issue and I agree with Simon that it should 
not allow nor encourage RFC violations.

Roy