Dynamic (changing) IPv6 prefix delegation

Mon Nov 21 20:27:55 UTC 2011

On Nov 21, 2011, at 7:21 AM, Seth Mos wrote:

> Hello List,
> 
> As a pfSense developer I recently ran into a test system that (actually)
> gets a IPv6 prefix from it's ISP. (Hurrah).
> 
> What is bewildering to me is that each time the system establishes a new
> PPPoE session to the ISP they assign a different IPv6 prefix via
> delegation together with a differing IPv4 address for the WAN.
> 
> Is this going to be forward for other consumer ISPs in the world?
> 

Unfortunately, there are some ISPs that believe this is the right thing to do.
Some go so far as to claim that scrambling customer prefixes is a mechanism
to help insure customer privacy.

> One of the thoughts that came to mind is T-Online in Germany that still
> disconnects it's (PPPoE) user base every 24 hours for a new random IP.
> 
> Short of setting really short timers on the RA messages for the LAN I
> can see a multitude of complications for consumers in the long run.
> 

Yep... It remains to be seen whether they will persist in this ill-conceived
behavior after the support calls start rolling in.

> People that configure their NAS, Media Player and Printer on their own
> network. And using ULA for either is not workable unless they somehow
> manage to grow DNS skill on the end user. Their NAS probably wants to
> download from the 'net and access videos from the NAS. The media player
> wants to be able to access youtube and the laptop needs to (reliably)
> find it's printer each time.
> 

I suspect that mDNS/Rendezvous will become much more widespread in
the IPv6 household and will become the primary service discovery
mechanism. It actually works quite well and is relatively resilient to either
frequent renumbering or the ill-advised use of ULA.

> I really hope that ISPs will commit to assigning the same prefix to the
> same user on each successive connection.
> 

It would be nice, but, I suspect there will always be some fraction of residential
ISPs determined not to do the right thing.

Look at the number that are refusing to make generous prefix allocations
to residential end users and limiting them to /56, /60, or even worse, /64.

Owen