Dynamic (changing) IPv6 prefix delegation

Mon Nov 21 16:33:59 UTC 2011

Seth Mos <seth.mos at dds.nl> writes:

> 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?

I certainly hope not.

But you should be prepared to handle the situation anyway.  Even those
ISPs providing a stable prefix may have to change it from time to time.
Which means that there is always a risk that the prefix changes with a
new PPPoE session, even if that doesn't happen every time.  And if the
prefix does change, then the old prefix will most likely not be routed
out the new PPP interface even if the lease hasn't expired yet.

You'll probably want to deprecate the old prefix when this happens,
signalling to the hosts that they should prefer the new prefix for new
sessions. 

Bjørn