Hi Simon,

unfortunately that problem is seen often with providers in Germany, although 
the large ones no longer do it (or allow to disable the disconnect). The 
problem is that German providers automatically disconnect the PPPoE connection 
every 24 hrs. After reconnecting you get a new address (IPv4) and prefix 
(IPv6). Since the changes we did (deprecating prefixes) this works fine  for 
standard router advertisements. But won't help for DHCPv6.

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" prefixes for some time when it figures out that 
the prefix changed and sends the new prefix at the same time. This allows to 
have no interruption (except the forced PPP disconnect). In general, in IPv6 
world you should forget about static addresses, it's also better for privacy.
- Alternatively use a very short DHCPv6 lease time. E.g., if router 
advertisements last a maximum time of 30 minutes, also set the lease time to 30 
minutes for IPv6. This requires clients to renew more often, but the change 
gots faster. If you force the router to disconnect during nights at a fixed 
time, the effect won't be so large.

Uwe

-----
Uwe Schindler
Achterdiek 19, D-28357 Bremen
http://www.thetaphi.de
eMail: u...@thetaphi.de

> -----Original Message-----
> From: Dnsmasq-discuss <dnsmasq-discuss-boun...@lists.thekelleys.org.uk>
> On Behalf Of Simon Kelley
> Sent: Sunday, September 9, 2018 11:49 PM
> To: dnsmasq-discuss@lists.thekelleys.org.uk
> Subject: Re: [Dnsmasq-discuss] clients of DHCPv6 with constructed IPv6
> address range are not notified on address range change
> 
> Dnsmasq doesn't implement RECONFIGURE. It probably should. The main
> problem, from a quick look at the RFC, is that RECONFIGURE mandates use
> of security mechanism, and dnsmasq doesn't implement that either!
> 
> The intention is that address change is a gradual process. The old
> address gets deprecated whilst the new one is added, and after a while
> the old address disappears. DHCP lease times are shorter than the time
> taken for an address to disappear. This gives time for hosts to move to
> the new address.
> 
> What's happening in your case seems a bit brutal. Even if you can push
> the change to all the clients fast, you're still going to break every
> on-going connection at address-change time.
> 
> 
> Cheers,
> 
> Simon.
> 
> 
> 
> On 09/09/18 22:07, Andrey Vakhitov wrote:
> > Thanks for a great dnsmasq software.
> >
> >
> >
> > I’m using dnsmasq 2.79 in combination with IPv6 prefix delegation. The
> > prefixes are changing daily due to daily reconnect of upstream router.
> > Dhcpcd is used to handle prefix delegation on external interface and
> > apply new address to internal interface (dmz0). Dnsmasq picks up the
> > prefix assigned to the internal interface by dhcpcd and server RA and
> > DHCPv6 server.
> >
> >
> >
> > dhcp-range=set:dmz6,::,constructor:dmz0,ra-stateless,ra-names
> >
> > dhcp-
> host=id:00:02:00:00:ab:11:9b:74:21:c0:e9:5d:1c:18,set:dmzfix6,[::56],dmzhos
> t
> >
> >
> >
> > Initially the host gets IPv6 address via DHCPv6 correctly, DNS
> > resolution works as expected, everything seems to be ok. But after
> > reconnect (and according prefix change) the client stays with the IPv6
> > address from old prefix and doesn’t update it. I’ve used tcpdump to
> > monitor DHCP-related traffic and could not see DHCPv6 RECONFIGURE
> > message sent by dnsmasq to clients on prefix change. I assume that this
> > is the cause of the problem: DHCP clients are not aware of changed
> > prefix and can’t act without corresponding notification from server.
> >
> > As dhcp client I use build-in DHCP client from system-networkd, just for
> > info, maybe it matters…
> >
> >
> >
> > If I’m wrong with my assumption I’d appreciate any explanation helping
> > me to configure dnsmasq and DHCP client properly.
> >
> >
> >
> > Best regards,
> >
> > --
> >
> > Andrey Vakhitov
> >
> >
> >
> > E-Mail:  and...@vakhitov.net <mailto:and...@vakhitov.net>
> > Stuttgart, Germany
> >
> >
> >
> >
> >
> > _______________________________________________
> > Dnsmasq-discuss mailing list
> > Dnsmasq-discuss@lists.thekelleys.org.uk
> > http://lists.thekelleys.org.uk/mailman/listinfo/dnsmasq-discuss
> >
> 
> 
> _______________________________________________
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> Dnsmasq-discuss@lists.thekelleys.org.uk
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