[Dnsmasq-discuss] [PATCH] DHCPv6: Add support for more than one hardware address per IPv6 address

Simon Kelley simon at thekelleys.org.uk
Mon May 22 23:11:02 BST 2017

On 12/05/17 16:32, Pali Rohár wrote:
> On Friday 12 May 2017 17:15:20 Simon Kelley wrote:
>> There are so many layers of quotes here that I've completely lost
>> track of what we were trying to achieve, and how to achieve it. My
>> memory is that we'd failed to come up with any consensus on either
>> of those.
> Goal 1:
> Ability to assign one IPv4 address to two different MAC addresses. 
> Currently it is possible by misusing concept of "more mac addresses" 
> (where IPv4 address can be "steal" by later DHCP client).
> Goal 2:
> Achieve Goal 1 also for DHCPv6.
>> Using MAC addresses with DHCPv6 AT ALL is quite difficult - it's not
>> a concept that the RFCs deal with.
> I read DHCPv6 RFC and it does not refuse assigning IPv6 address based on 
> link layer MAC address. Anyway, this is already supported by dnsmasq.
> But what I want to achieve has ability to assign one IPv6 address to 
> more MAC addresses at same time. This DHCPv6 RFC does not allow, but in 
> some situations it is useful and I think such options could be provided 
> by DHCPv6 server with explicit warning in documentation.
>> Doing the sleight-of-hand trick
>> that works with DHCPv4 doesn't seem feasible to me for DHCPv6.
> Do you completely disagree with fact that dnsmasq could support this 
> scenario for assigning one IP address to more network cards (identified 
> by MAC address)? Or you just do not like my current implementation?

The whole point of DHCP is to avoid an IP address being used by more
than one network card. The current two-MAC addresses for one IP facility
in DHCPv4 doesn't contradict this. It's specified to be used only when
there's a guarantee that both MAC address are never simultaneously in use.



> In previous email I wrote that Goal 2 can be achieved by storing tuple 
> DUID, IAID, MAC address and IPv6 address into DHCPv6 leases file.

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