[131662] in North American Network Operators' Group
Re: Failover IPv6 with multiple PA prefixes (Was: IPv6 fc00::/7
daemon@ATHENA.MIT.EDU (Owen DeLong)
Mon Nov 1 00:30:46 2010
From: Owen DeLong <owen@delong.com>
In-Reply-To: <20101101024339.B716B62B8AB@drugs.dv.isc.org>
Date: Sun, 31 Oct 2010 21:25:33 -0700
To: Mark Andrews <marka@isc.org>
Cc: NANOG list <nanog@nanog.org>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
On Oct 31, 2010, at 7:43 PM, Mark Andrews wrote:
>=20
> 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.
>>>=20
>>> I have a few candidate networks for it. =3DA0Mostly networks used =
for
>>> clustering or database access where they are just a flat LAN with no
>>> "gateway". =3DA0No layer 3 gets routed off that subnet and the only =
things
>>> talking on it are directly attached to it.
>>=20
>> why not just use link-local then?
>=20
> If you had actually every tried to use link-local then you would know =
why
> you don't use link-local.
>=20
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.
>=20
> 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].
>=20
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.
>=20
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
