Failover IPv6 with multiple PA prefixes (Was: IPv6 fc00::/7 - Unique local addresses)

Owen DeLong owen at
Tue Nov 2 11:03:33 CDT 2010

On Nov 2, 2010, at 4:55 AM, Karl Auer wrote:

> On Tue, 2010-11-02 at 10:51 +0000, Tim Franklin wrote:
>>> That breaks the IPv6 spec. Preferred and valid lifetimes are there
>>> for a reason.
>> And end-users want things to Just Work.  The CPE vendor that finds a
>> hack that lets the LAN carry on working while the WAN goes away and
>> manages to slap the "With Home Network Resilience!" label on the box
>> correctly will presumably do quite nicely out of it.
> But - preferred and valid lifetimes do *exactly that*. The address is
> fully usable up to the end of the preferred lifetime. It is then
> deprecated (but not unusable) until the end of the valid lifetime. Only
> after the valid lifetime does it become unusable. DHCPv6 lifetimes are
> exactly the same as RA lifetimes - and of course there is nothing that
> says the RA lifetimes have to be the same as the DHCPv6 lifetimes
> (though some sensible relationship would be advisable).
> So loss of connectivity to the upstream is not going to blow away a home
> network. It will keep working fine, even if the upstream goes away for a
> while. It's up to the upstream to use lifetimes that are a good
> compromise between flexibility and stability.
> About the only hack I can see that *might* make sense would be that home
> CPE does NOT honour the upstream lifetimes if upstream connectivity is
> lost, but instead keeps the prefix alive on very short lifetimes until
> upstream connectivity returns.
Which is exactly what was being proposed when Tim responded that it
would break the IPv6 spec.


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