moving to IPv6

Karl Denninger karl at Mcs.Net
Tue Nov 4 05:14:22 UTC 1997

On Mon, Nov 03, 1997 at 08:53:11PM -0800, Pedro Marques wrote:
> > If IPv6 allocations will have varying sizes like CIDR, then we might
> > continue to have issues of size based route filtering.  OTOH, with the
> > right methods of allocating IPv6 space, no one should ever have to come
> > back to get more space.  Eventually that should mean fewer routes as
> > IPv4/IPv6s4 closes down.  Route filtering should be encouraged on IPv4
> > space and prohibited on IPv6 space, at that point, IMHO.
> I don't think i really understand your point here....
> The only "difference" when it comes to routing information i can think off
> is that in IPv6 there isn't suppose to be address ownership (which creates
> holes into CIDR blocks)... but it seems to me that the same policy is
> being adopted for IPv4.
>   Pedro.

Bad model.  I said this years ago.

IPng needs to have enough *prefix* length that every autonomous system
currently in existance or which will come into existance during its lifetime
can have a *unique*, *single* prefix.

Then the whole address ownership issue becomes moot - each ASN becomes a
prefix (heh, now that's novel - why not just use the ASN - duh!) and the
remaining space (define it as 32 bits for backward compatibility reasons
with IPv4) is private to the ASN.

If you change ASNs as a customer, it is between you and the new provider
whether you need to renumber - the rest of the world *DOES NOT CARE*.

What this leads to is a registry system (one or more) for the 32-bit
suffixes in which you form "colloquial" memberships, ensuring uniqueness
among competing ASNs *as long as both ASNs subscribe to the same registry*.

But membership is VOLUNTARY; you give up nothing except possibly the ability
to allow people to join your ASN without renumbering if you don't belong.

Right now membership in these registries is MANDATORY; the network breaks if
you choose random 32-bit integers and masks and announce them.  We can fix
this if we think for more than 2 nanoseconds before doing something stupid

If you want to connect to an ASN which is *NOT* part of your colloquial
group, that's fine too -- but you might need to renumber in that case (or 
perhaps not - 32 bits is still quite large).

With each ASN having 32 bits of *private* address space, the IP space becomes
effectively infinite, and the route table size is fixed at one entry per ASN.

The best of both worlds.

This is also, by the way, trivially backward compatible (heh, what a concept);
bitwise masking provides all you need to translate between local and global
address formats (these operations are extremely fast, and typically
single-instruction-cycle in duration on modern processors).  Hardware
bit-slice assist on interface boards make it cheap and feasible even at
wire rates to translate at the boundaries of an ASN both inbound and

This kind of logical design, of course, cannot be allowed to happen within
the realm of the Internet, which is why we'll never see it in our lifetime.

It never ceases to amaze me how people will ignore the obvious solutions to
problems like this.

Karl Denninger (karl at MCS.Net)| MCSNet - Serving Chicagoland and Wisconsin     | T1's from $600 monthly to FULL DS-3 Service
			     | NEW! K56Flex modem support is now available
Voice: [+1 312 803-MCS1 x219]| 56kbps DIGITAL ISDN DOV on analog lines!
Fax:   [+1 312 803-4929]     | 2 FULL DS-3 Internet links; 400Mbps B/W Internal

More information about the NANOG mailing list