[Dnsmasq-discuss] WG: clients of DHCPv6 with constructed IPv6 address range are not notified on address range change

[Simon Kelley]

On 15/09/18 10:05, Andrey Vakhitov wrote:
> Hello Uwe,
> 
>>> My recommendation to the reporter:
>>> - Don't use stateful DHCPv6 in Germany, that does not work well. You 
>>> clients should get the addresses using router advertisements. For static
> hosts assign static names in your own domain. The "ra-names"
>>> assigns both the IPv4 and IPv6 address to the SLAAC name, so lookup 
>>> works fine. With router advertisements, DNSmasq will send "deprecated" 
> 
>> As you correctly recognized, the reason for usage of stateful DHCPv6 was
> to get correct dynamic name resolution for IPv6. 
>> I also see the combination of DHCPv4 with SLAAC as possible workaround,
> I've to try it
> 
> I've set it up as you suggested, initially name resolution seems to work
> fine. But after some days of operation (and some nightly reconnects) dnsmasq
> seems to loose associated IPv6 adresses: DNS request reports only IPv6
> address assigned via DHCP. The SLAAC-based IPv6 addresses on hosts are
> present and correct. How can I investigate and fix this issue?


Hmm, not easy.

Look in the log for lines that look like

DHCPv4-derived IPv6 names on ........

which should occur after a reconnect with a different address which
causes new DHCP address ranges to be constructed.

After that happens, dnsmasq will take a guess at the IPv6 addresses that
hosts will assign themselves, based on the network address and the MAC
address of the host (transformed into EUI-64) It then starts to ping
those addresses, and when it gets a reply, it will log

SLAAC_CONFIRM(interface) <address> <hostname>


and start using the address/name in the DNS.

Once confirmed, the addresses remain valid until the DHCPv4 lease it's
based on expires or goes though init-reboot state or the MAC address or
interface it's accessible by changes.

The only other thing that will delete these addresses in a new address
appearing and a new dhcp range being created, hence it's interesting to
look at what happens in the logs after each of those events.



Cheers,

Simon.

> 
> Best regards,
> --
> Andrey Vakhitov
> 
> E-Mail:  andrey at vakhitov.net            Stuttgart, Germany
> 
> 
> 
> 
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