[OpenWrt-Devel] DHCPv6 flash renumbering patches with HE tunnel breaks

Arjen de Korte arjen+openwrt at de-korte.org
Thu Mar 26 15:38:50 EDT 2015

Citeren Steven Barth <cyrus at openwrt.org>:

>> This breaks clients that need fixed IPs (in my case, mostly webmail  
>> clients).
> I wonder why they are so sensitive to source-address changes since  
> their old address is still valid and not deprecated so there is no  
> need to switch.

Webmail clients usually don't keep a connection open to the server,  
hence every connection is a new one. The webmail server only sees the  
source IP, so even if the DHCPv6 address is still valid for the  
client, a re-login is needed because the source IP changes.

> I would gladly send the DHCPv6 address with 0 preferred lifetime but  
> Apple's DHCPv6 client has issues and discard addresses therefore the  
> 1.
>> I could create a patch for this, but for now I consider this a  
>> regression, rather than a feature that needs to be configurable. I  
>> fail to understand the reasons why this change, which deliberately  
>> breaks the outgoing addresses (even if only momentarily) was  
>> introduced.
> The reason for this change is that no host seems to support DHCPv6  
> reconfiguration so we cannot update clients whenever we see fit  
> (e.g. ISP goes down / is switched / designates a different PD).  
> Which means that in absence of that in worst case client  
> connectivity is lost for T1 seconds.

I don't see how this fixes things then. When ra_management is '2'  
you'd still run into the exact same problem (just without the fallback  
to SLAAC). In contrast, if the ip6prefix is configured statically (as  
in my case), there is no chance this will ever happen, since changes  
will never happen unexpectedly.

I think this would be much better fixed by making the client renew its  
lease more frequently (by lowering the valid and preferred lifetimes).  
The present fix will also not work for anthing else than a /64.
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