Using IPv6 with prefixes shorter than a /64 on a LAN

Mark Andrews marka at isc.org
Sat Feb 5 20:40:51 CST 2011


In message <4D4DF75E.1040109 at brightok.net>, Jack Bates writes:
> On 2/5/2011 7:01 PM, Mark Andrews wrote:
> > And did you change the amount of growth space you allowed for each pop?
> > Were you already constrained in your IPv4 growth space and just restored
> > your desired growth margins?
> >
> Growth rate has nothing to do with it. ARIN doesn't allow for growth in 
> initial assignments. No predictions, no HD-Ratio, and definitely no 
> nibble alignments.
> 
> Current policy proposal hopes to fix a lot of that.
> 
> >> In the near future I expect to be somewhere between a /24
> >> and a /28, which is an 8 to 12 bit shift right from my IPv4 /16 allocation
> .
> > Only if you can serve all those customers from that /16.  You are
> > then not comparing apples to apples.  You are comparing a net with
> > no growth space (IPv4) to one with growth space (IPv6).
>
> Not sure I get ya here. I am comparing apples to apples. ARIN gives me a 
> /16 of space. There are the same number of /16's in IPv4 as IPv6. 
> However, in IPv6, they will allocate a /24 at most to me, and I will 
> never exceed that. This shift of 8+ bits is the gains we get shifting 
> from IPv4 to IPv6.

A IPv4 /16 supports 64000 potential customers.  A IPv6 /32 supports
64000 potential customers.  Either you have changed the customer
estimates or changed the growth space allowances or were using NAT
or ....

You don't suddenly need 256 times the amount of space overnight all
other things being equal.  About the only thing I can think of is
you need to advertise 256 routes and you are asking for extra blocks
to get around poorly thought out filtering policies.

A routing slot is a routing slot.  It really doesn't matter if that
slot has a /32 or a /40 or a /48 in it.  They are equally expensive.

If ISPs were being honest and matching IPv4 to IPv6 filtering the
filters would be set a /40 not /32.  By setting the filters to /32
you force the small ISP to ask for up to 256 times as much address
space as they need with absolutely no benefits to anyone just to
get a routing slot that won't be filtered.

What's really needed is seperate the routing slot market from the
address allocation market.

Mark

> Jack
-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: marka at isc.org




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