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

[Owen DeLong <owen () delong com>]

On Oct 31, 2010, at 7:43 PM, Mark Andrews wrote:

> In message <AANLkTimsB6Uj-jpogLg08Q-RZDUB-+C9c5KMzcKTQKmQ () mail gmail com>, Chri
> stopher Morrow writes:
> > On Sun, Oct 31, 2010 at 2:01 PM, George Bonser <gbonser () seven com> wrote:
> > > > ula really never should an option... except for a short lived lab,
> > > > nothing permanent.
> > >
> > > I have a few candidate networks for it. =A0Mostly networks used for
> > > clustering or database access where they are just a flat LAN with no
> > > "gateway". =A0No layer 3 gets routed off that subnet and the only things
> > > talking on it are directly attached to it.
> >
> > why not just use link-local then?
>
> If you had actually every tried to use link-local then you would know why
> you don't use link-local.
I use link local often for many things. Try again.

> > eventually you'll have to connect
> > that network with another one, chances of overlap (if the systems
> > support real revenue) are likely too high to want to pay the
> > renumbering costs, so even link-local isn't a 100% win :(
> > globally-unique is really the best option all around.
>
> 2^40 is 1099511627776.  The chances of collision are so low that
> one really shouldn't worry about it.  You are millions of times
> more likely of dieing from a asteroid 1-in-500,000[1].
There are almost 7,000,000,000 people on the planet. We have
not had anywhere near 14,000 people killed by asteroids, I
think their calculation is off.

> If you merge thousands of ULA and don't consolidate then you start
> to have a reasonable chance of collision.  Even if you do have
> colliding ULA prefixes you don't necessarially have colliding subnets
> when merging companies.  Just allocate subnet randomly.  It's not
> like 2^16 internal subnets is going to be a major routing problem.
This is, of course, assuming many things:

        1.      Everyone follows the same random ULA allocation algorithm.
        2.      The algorithm is not flawed and yields relatively smooth
                distribution without significant hot-spots.
        3.      People are not lazy
        4.      People read instructions

Assumption 1 depends on assumptions 3 and 4.
Assumption 2 is still relatively unknown as we don't have enough operational
experience with it.
Assumption 3 is pretty well provably false.
Assumption 4 is virtually guaranteed to fail.

Since Assumptions 3 and 4 are non-starters, assumption 1 is seriously flawed
at best.


Owen