[Dnsmasq-discuss] Additional feature requested for stateful DHCHv6 together with a 6RD-tunnel to the ISP

[Joakim Langlet]

fre 2013-01-11 klockan 10:22 +0000 skrev Simon Kelley:
> On 10/01/13 23:41, Joakim Langlet wrote:
> > I have configured a Raspberry Pi as a dual-stack (IPv4/IPv6) internet
.....
> > 
> 
> This problem has been noticed before, and I've been working with the
> OpenWRT people on a different solution available in the current 2.66test
> series of releases.
> 
> It works like this: instead if specifying complete IPv6 addresses in a
> DHCP range, the start and end addresses are just the host-identifier
> part. There's an additional keyword which specifies an interface name.
> An example makes this clearer.
> 
> dhcp-range=::1,::400,constructor:eth0,.......
> 
> This tells dnsmasq to watch eth0 for addresses with host-identifier part
> ::1, and when it sees one, to create a dhcp-range using the prefix from
> that address.
> 
> So, in your case, when the DHCPv4 address is assigned, the machinery
> attached to the the DHCPv4 client creates the 6RD prefix (say,
> 2001:db8:c000:0264) and adds the address
> 2001:db8:c000:0264::1 to eth0. Dnsmasq notices this automatically, and
> creates a live dhcp-range=2001:db8:c000:0264::1,2001:db8:c000:0264::400
> 
> The system will cope with multiple addresses, also old addresses
> disappearing and it uses the preferred lifetime of the address in the
> interface to deprecate addresses before they disappear. This all works
> for both stateful DHCPv6 and router-advertisements, and even the
> ra-names RA naming mode. (It's quite fun to add a new address to the
> interface and see a new IPv6 address instantly appear in the DNS for
> existing hosts.)
> 
> 
> I'm happy to hear comments on my solution, and argue about which of
> these methods is better: I think the interface-watching system is easier
> and neater to configure, but it's less flexible than the
> macro-replacement method and specifically doesn't handle dhcp-host. I
> confess I hadn't considered the need to do that, but I can see it would
> be useful. Something similar could be incorporated into the
> interface-watching system. The exact semantics are tricky: what happens
> to existing leases when a dhcp-host which depends on a 6RD prefix
> disappears?
> 
> You can try the new code in 2.66test. The last few releases have
> unrelated  show-stopping bugs, so it's probably best to try 2.66test5
> until we get those ironed out.
> 
> Cheers,
> 
> Simon.
> 
> 
> 
> 
> 
> 
> 
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I guess that this could solve part of the issue and I will of course
have a look at it.

As you mentioned, "dhcp-host" would still not be supported. I would like
to use dhcp-host in order to allow certain services (located on a
specific machine) to get a "deterministic" IPv6 address, so that I
change the "AAAA" record in the public DNS out-there.
By using this mechanism, I would not have to administrate the address
change on the server, but I guess that a defined "lease-time" (which is
short) would be required. BTW: Can the lease-time be set for
dhcp-host?? 

There are of course other ways to accomplish the same thing, but
dhcp-host with "prefix substitution" seems to be a neat solution.

Any solution that would allow both dhcp-range and dhcp-host to be
updated when the address changes, is the solution that I would vote for.

Again, I will have a look at 2.66test5 to see how that works...

Cheers,
Joakim