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

Christopher Morrow morrowc.lists at
Sun Oct 31 20:32:39 CDT 2010

On Sun, Oct 31, 2010 at 3:10 PM, David Conrad <drc at> wrote:
> On Oct 31, 2010, at 6:45 AM, Christopher Morrow wrote:
>>>> "If Woody had gone straight to a ULA prefix, this would never have happened..."
>>> Or better yet, if Woody had gone straight to PI, he wouldn't have this problem, either.
>> ula really never should an option... except for a short lived lab, nothing permanent.
> Seems to me the options are:
> 1) PI, resulting in no renumbering costs, but RIR costs and routing table bloat
> 2) PA w/o ULA, resulting in full site renumbering cost, no routing table bloat
> 3) PA w/ ULA, resulting in externally visible-only renumbering cost, no routing table bloat
> Folks appear to have voted with their feet that (2) isn't really viable -- they got that particular T-shirt with IPv4 and have been uniformly against getting the IPv6 version, at last as far as I can tell.
> My impression (which may be wrong) is that with respect to (1), a) most folks can't justify a PI request to the RIR, b) most folks don't want to deal with the RIR administrative hassle, c) most ISPs would prefer to not have to replace their routers.
> That would seem to leave (3).
> Am I missing an option?

I don't think so, though I'd add 2 bits to your 1 and 3 options:
1) we ought to make getting PI easy, easy enough that the other
options just don't make sense.
2) ULA brings with it (as do any options that include multiple
addresses) host-stack complexity and address-selection issues... 'do I
use ULA here or GUA when talking to the remote host?'


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