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

[Pali Rohár]

(after two months) PING!

On Wednesday 27 January 2016 13:37:27 Pali Rohár wrote:
> On Wednesday 20 January 2016 20:15:23 Simon Kelley wrote:
> > Dnsmasq identifies IPv6 clients via their MAC address for the purpose
> > of selecting dhcp-host configuration to use, but it doesn't use the
> > MAC address as a unique client identifier for the purpose of assigning
> > DHCP leases in the same way the DHCPv4 does. That's the crucial
> > difference.
> 
> Yes, I know.
> 
> > The equivalent of the DHCPv4 share MAC address facility, should really
> > be something  which shares IAIDs, maybe?
> 
> Right, in lease file is stored pair (MAC address, IP address) for IPv4
> and pair (IAID, IPv6 address) for IPv6.
> 
> > The crucial thing I'm trying to achieve here is turning your patch
> > from something that works on your network, with your very odd
> > configuration, into something that other people might want and use.
> > Without that, it's fine as your patch, but it can't go into the
> > dnsmasq mainline.
> 
> Understood.
> 
> > Maybe the way to think about that is to think about
> > how to document it. If we can describe what problem it solves, and how
> > it should be used, then we'll be getting there.
> 
> I was thinking about it for more days. It is really not easy to solve
> this problem... Here are my results:
> 
> * There are people who misuse original concept of "more mac addresses"
>   for one ipv4 address. Dnsmasq supports this configuration only if one
>   mac address from that --dhcp-host line is used at same time.
> 
> * DHCPv6 clients are identified by DUID string, which we can say is
>   totally random and are not persistent across multi-OS computers or
>   reinstalling...
> 
> * Internally DHCPv6 leases are identified by IAID.
> 
> So to make configuration clean for both IPv4 and IPv6 we need support for:
> 
> * Assigning IPv4 lease to more MAC addresses at the same time
>   (This will help people to use "more mac addresses" functionality correctly)
> 
> * Assigning IPv6 address to more DUIDs at the same time
>   (This is "correct" IPv6 equivalent for previous request)
> 
> * Assigning IPv6 address to more MAC addresses at the same time
>   (This is what would fix DUID problem)
> 
> And it means that pair (IAID, IPv6 address) for IPv6 leases it not
> enough to do it.
> 
> So, what about extending lease line for IPv6 addresses to include DUID
> and MAC address?
> 
> > We need to bear in
> > mind that the behaviour we're talking about violates the RFCs
> > specifying DHCPv6, so it has to be especially carefull justified.
> 
> Thats probably truth, but if something is useful users will try to use
> it. Either itself by patching dnsmasq or if possible by optional config
> options...
> 

-- 
Pali Rohár
pali.rohar at gmail.com