ISP customer assignments

Wed Oct 14 01:12:32 UTC 2009

On Tue, Oct 13, 2009 at 6:34 PM, Cord MacLeod <cordmacleod at gmail.com> wrote:

> IPv4?  What's the point of a /64 on a point to point link?  I'm not clear

IP Addressing uniformity and simplicity.

Use of  /127s  for   Point-to-Point  links  introduces  addressing
complexity that may be avoided  in V6:  the scarcity of  IPs
necessitated it in V4 .    At least  /112   lies on an  even 16-bit
boundary, and that makes it  the longest prefix that is a very good
choice,  if you do need a non-standard mask.

Unless you have only a /32  of V6 space and  1 billion P2Pt links you
need (or similar scenario), there is no  utility in  practicing
rampant prefix length expansion, for the purpose of conservation
(there may be other reasons  such as preventing autoconfig).

> For all intensive purposes a /126 translates to a /30
> in IPv4.  Do people assign /24's to their point to point links today with

Not really;  there's a massive difference of scale.    Say there's a
big vat that contains all gold in the universe,  you get to bring home
one  bucket of gold flakes to allocate to your customers.

In the V4 universe, well you got a /19..   You got a 60 kilogram
bucket,  and a /30  represents a 1  troy ounce scoop  taken out of
that bucket..

In the V6 universe, even if you got a measly /48:   one   /64  from that
is a 1 troy ounce gold flake out of your  2000  kilogram bucket.
Should you really be worried about cutting up that flake?

In reality... if you're an ISP the worst you have is a /32,  you can
think of a  /48  that way,   you do have  65536 of those  /48s,  also
known as a
133,588,416kg  bucket,  since  your  /32   has a maximum of   4 billion  /64s.

Normally when you have a P2P link,  it will mean you connect an end
site also: that end site gets a  /48   (Per the justification that
allows you as an ISP to get a /32,  such a large allocation).   After
assigning  65536  /64s, or 256  /64s  (if you give out /56s  to end
sites)  which you already do for each _end site_ as
standard address allocation  practice in V6,  what's another  single
/64,  seriously?

--
-J