[131724] in North American Network Operators' Group
Re: Failover IPv6 with multiple PA prefixes (Was: IPv6 fc00::/7 -
daemon@ATHENA.MIT.EDU (Owen DeLong)
Tue Nov 2 12:04:55 2010
From: Owen DeLong <owen@delong.com>
In-Reply-To: <1288698921.12974.292.camel@karl>
Date: Tue, 2 Nov 2010 09:03:33 -0700
To: Karl Auer <kauer@biplane.com.au>
Cc: nanog@nanog.org
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
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.
Owen
