I-D Action:draft-azinger-scalable-addressing-00.txt

Mark Smith nanog at 85d5b20a518b8f6864949bd940457dc124746ddc.nosense.org
Wed Sep 29 07:37:39 CEST 2010

On Wed, 29 Sep 2010 09:48:17 +1300
Brian E Carpenter <brian.e.carpenter at gmail.com> wrote:

> On 2010-09-29 03:58, Michael K. Smith - Adhost wrote:
> ...
> > 
> > I'm trying to wrap my brain around how PA space is going to be "better" than PI space.  Follow my potentially flawed logic.
> > 
> > - I have a /32 that I announce through my various upstreams - no more specifics, just one /32.
> > - I get a /48 from my upstream out of their /32.  I announce my /48 through my various providers
> > - I pressure my provider into announcing my /48 as well for traffic engineering
> > - Now we have a /32 and a /48 in the table.
> > - Rinse, repeat
> > 
> > How is this better?  Is it really anyone's assumption that I should be forced into a one-upstream solution and that I would find that acceptable? 
> Tony replied correctly, and indeed I teach graduate students that it isn't
> better, so it must be true :-).
> To be clear, the classical model for scalable PA-based multihoming in IPv6
> is and always was that a multihomed site would simultaneously operate a
> different PA prefix from each of its ISPs and each host would simultaneously
> have N addresses, one for each of those ISPs. Whether you like it or not,
> this works perfectly and allows complete aggregation. Shim6 was designed to
> provide for session survival in that situation. This works too.
> The problem is, site IT managers don't seem to like this model and its
> implication of renumbering when you add or drop an ISP.

I think one of the key things they may not realise, probably
because they are just treating IPv6 as nothing more than IPv4 with
bigger addresses, is that there is a transition period where the old
addresses are phased out, potentially over a number of weeks or months.
They probably assume it is an instant event that doesn't give them any
preparation time to manage the process of e.g. updating ACLs, router
interface configurations etc.

It'd be interesting to specifically ask these IT managers, when they
express this opinion, if they're aware of the IPv6 address valid and
preferred lifetime mechanisms, and how they were planned to be used to
cope with a renumbering event. It'd also be interesting to ask them if
they're aware of ULA addresses, and how they are designed to facilitate
stable internal communications regardless of whether global address
renumbering is happening or not.

I sometimes wonder if a lack of awareness or understanding of IPv6's
capabilities is the actual cause of some of the objections to it.

> (Whether ISPs
> like it or not is somewhat irrelevant, because they have no say in whether
> a site chooses to operate this way. Even the fact that it messes with
> current methods of BGP-based traffic engineering is not an objection
> that ISPs can force onto site IT managers.)
> Hence, the RRG work, LISP, ILNP, etc. Been there, discussed that, and
> here we are with PI as the only deployed alternative. Grumble.
>     Brian


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