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Re: Shim6 vs PI addressing

  • From: Mark Newton
  • Date: Thu Mar 02 06:06:19 2006

On Thu, Mar 02, 2006 at 02:21:45AM -0800, Owen DeLong wrote:

 > Yes, I am well aware of 32bit ASNs.  However, some things to consider:
 > 1.	Just because ASNs are 32 bits doesn't mean we'll instantly
 > 	issue all 4 billion of them.  The reality is that we probably
 > 	only need about 18 bits to express all the ASNs well need for
 > 	the life of IPv6, but, 32 is the next convenient size and there's
 > 	really no benefit to going with less than 32.

It's probably worth using this juncture to point out that exactly
the same principle applies to the bit-width gap between IPv4 and IPv6:
the fact that IPv6 gives 128 bits doesn't mean we're going to allocate
all of them right away.

The number of networks in use is not driven by the size of the 
address space;  it's driven by the number of enterprises who wish
to connect to the Internet, the number of sites at which they wish
to connect, the number of interfaces they wish to use to carry
out their interconnections, and the number of hosts they're bringing
along with each connection.

Notice that none of that has anything to do with the version number
of the protocol which those hosts are speaking.  By any way you 
measure it, Internet growth is a function of end-user demand, not
a function of the number of bits in an IP address.

We can spend another decade talking about how to manage routing
table growth if we really want to, but during that decade the
routing table is going to *keep growing anyway*.  If we want to
prevent it from growing, the only real way to do it is going to
be at the demand side -- which is another way of saying that we'd
need to address and control all of the clauses I iterated through
two paragraphs ago. 

When you distill *that* message to its essence, you can restate it
like this:

  "We can control the growth of the IP routing table by making 
  it harder for people to connect their networks to the Internet."

Because that's what the advocates for IPv6 universal PA space 
are *really* saying, once you remove all the smoke and mirrors.

... which neatly explains a major reason for why IPv6 hasn't taken
off, and why shim6 remains vapourware despite many years of discussion
and the presence of a clear, unambiguous demand for a solution
to the multihoming problem.

What's the way out?  Acknowledgement of the fact that the size
of the routing table is a function of the size of the Internet.
Y'know, one of those "duh!" statements.  If we expect the Internet
to grow past 32-bit limitations, we're going to have to expect
the routing table to grow past the constraints which that 32-bit
world has imposed upon it.  Solving *that* problem is, IMHO,
overwhelmingly preferable to breaking multihoming and handing
routing policy decisions over to the viruses and worms which
control each host.

(note that I'm not pretending that solving the routing table
growth problem is -easy-, it's just plainly obvious to me that
it'll need to be solved anyway, and the IPv6 PA advocacy that
keeps coming up seems to be an exercise in denial...)

  - mark

Mark Newton                               Email:  [email protected] (W)
Network Engineer                          Email:  [email protected]  (H)
Internode Systems Pty Ltd                 Desk:   +61-8-82282999
"Network Man" - Anagram of "Mark Newton"  Mobile: +61-416-202-223