Another v6 question

Max Pierson nmaxpierson at
Tue Jan 25 15:43:01 CST 2011

Great reply's on and off-list so far.

To hit on a few points ...

Owen, thank you for catching my terminology blunder there. I understand
smaller is != shorter. Complete mistake :)

Glad to see most have loosened that policy, as I figured it wouldn't hold at
the time I originally heard it 2 or so years ago.

>You really can't map prefix availability to prefix usage.
>There are 4 billion IPv4 /32s. There aren't 4 billion LIRs that will get

I wasn't exactly mapping prefix availability to usage, apologies if it came
across like that. My crunching did not include host bits. I understand I
won't see /64's from each of my neighbors down the street. (or I shouldn't

>As to the IPv4 de-agg, I think that's going to be one of the primary causes
>an accelerated deprecation of IPv4 once IPv6 starts to become more

I would agree from a SP perspective, however from and end-user and
enterprise perspective, most don't care about table sizes and will be slow
to move to v6 until "everyone else is doing it" ... (as in they have to now
because their facebook status won't be offered over v4 anymore). Alot
of organizations I've spoken with still don't know what v6 even is. I think
alot of end-user land and even some enterprises will drag their feet on this
as long as it costs money for hardware upgrade to support v6, also having
staff to support v6, legacy v4 apps that won't be ported to v6, etc. (I
understand there's ways around this, my point is the customer doesn't). I
think v4 will be around longer than we want it to (unfortunately), but time
will tell.

To Jusin's point,
I agree that we will be net-negative for a while. My concerns is trying to
dual-stack a v4 table and a v6 table. They both will grow over time, and
until the powers that be "pull the plug" on re-issuing returned v4 space
(which I completely disagree with), it'll continue that way. That's just my
opinion though :)

Once again, thanks for all on and off list responses!

On Tue, Jan 25, 2011 at 1:46 PM, Owen DeLong <owen at> wrote:

> On Jan 25, 2011, at 10:19 AM, Max Pierson wrote:
> > Hi List,
> >
> > Sorry to bring up yet ANOTHER v6 question/topic, but this seems to be one
> > that I cannot get a solid answer on (and probably won't and in the event
> > that I do, it will probably change down the road anyways), but here goes.
> >
> >> From the provider perspective, what is the prefix-length that most are
> > accepting to be injected into your tables??  2 or so years ago, I read
> where
> > someone stated that they were told by ATT that they weren't planning on
> > accepting anything smaller than a /32. So what if I get my shiny new /48
> > from ARIN and am already multi-homed??? Does ATT not want my business
> (which
> > they wouldn't get if the first place, but for argument sake, yes, I chose
> to
> > pick on ATT, sorry if I offended anyone :)  I already see /40's /48's
> ,etc
> > in the v6 table, so some folks are allowing /48 and smaller, so what is
> the
> > new /24 in v6?
> >
> Today, the vast majority of providers are accepting /48s in IPv6.
> Verizon was holding the line at /32 for a while, but, they moved to /48
> a few months ago.
> Let's be clear on terminology. I don't think anyone is allowing smaller
> than  /48, but, most are allowing /48 and shorter. (shorter prefix =
> bigger network).
> > I only ask due to the fact that ARIN's policy for end-users is /48
> minimum
> > (which is what i've been telling folks to apply for or applying for it on
> > behalf of them).
> >
> That's correct.
> > Second, as I was crunching a few numbers to get a rough estimate of what
> a
> > global table would look like in say 3 or 5 years after v4 is exhausted (I
> > understand that it's completely unpredictable to do this, but curiosity
> > killed the cat I guess), and in a few cases, I stopped due to the shear
> size
> > of the amount of prefixes I was coming with. Where i'm getting with this
> is
> > has anyone done any crunching on prefix count for v6 (as in estimates of
> > global table usage with the various prefix lengths seen above _based_ on
> the
> > initial allocation of the v6 space (not the entire v6 space itself)). I'm
> You really can't map prefix availability to prefix usage.
> There are 4 billion IPv4 /32s. There aren't 4 billion LIRs that will get
> /32s.
> There are 256 trillion IPv4 /48s (roughly). There are not 256 trillion
> end sites that will apply for /48s.
> The whole point of IPv6 is that the number of prefixes vastly exceeds
> the number of applicants that will use them.
> To measure the likely content of the IPv6 global table, then, we need
> to look at the number and type of users rather than looking at the
> maximum available number of prefixes.
> I haven't had trouble reaching anything I care about from my /48
> advertised through Hurricane Electric and Layer 42.
> > interested to see how long before we have 96Gb's of TCAM/Memory (take you
> > vendor of choice) in our routers just to take a full table. (Not to
> mention
> > still having all of the ipv4 de-agg crazyness going on today. Seriously,
> who
> > lets /28 and /32's in their tables today? And this will only get worse as
> v4
> > fades away).
> >
> Yeah, that's not likely to happen. TCAM doesn't scale that way. As to the
> IPv4 de-agg, I think that's going to be one of the primary causes for
> an accelerated deprecation of IPv4 once IPv6 starts to become more
> ubiquitous.
> Owen

More information about the NANOG mailing list