[arin-discuss] Trying to Understand IPV6

[Gary T. Giesen]

Darryl,

The first mistake you're making is trying to use IPv6 like IPv4.
Utilization for IPv6 is measured differently from IPv4.

One of the main goals of v6 addressing is aggregation, and to ensure
this, you should provide your customer with a large enough allocation
that they won't need a second one.

For most, this means a /48. Every customer is entitled to a /48, which
means they cna have up to 65536 *subnets*. In IPv6 each subnet is fixed
at a /64, so they will have 16 bits available to them for subnetting.

There is some debate over whether residential customers (the kind who
are typically running with a single IP and a NAT gateway right now)
should receive a /48 or a /56 (which still gives them 256 subnets), but
for anyone that qualified for anything larger than a /29 before (or any
type of business customer), definitely give them a /48.

All but the very largest ISPs will receive a /32, regardless of what
they have in IPv4. It may seem like a lot of hosts (and it is), but with
the fixed subnet size it's good to think of it differently. With a /32
(which leaves 32 bits for subnetting) *each* ISP will have more
*subnets* than all of IPv4 had IP *addresses*. Again, ARIN wants to
avoid ISPs coming back for a second allocation if possible.

So to answer your question, if you customer was eligible for a /21
before, then by all means give them a /48. They will be able to create a
ton of subnets, and should not have to go back for a second allocation
(which is the main strategy for IPv6).

GG

On Mon, 2010-09-13 at 13:24 -0400, Schnell, Darryl wrote:
> Can anyone recommend a good IPV6 website for Beginners? I’ve read
> about eight web sites which say the same things and I feel like my
> head is going to explode. I guess the problem I’m having is trying to
> understand how an IPv4 CIDR notation translates in an IPv6 CIDR in
> order to fill out ARIN IPV6 Allocation Template future usage section.
> My actual question is –
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> If I assigned a customer say an IPV4 /21 in IPV6 this would translate
> into a /56? If I’m not mistaken a /56 would translate into something
> like 65,000 host addresses? That just seems like a lot of hosts to me,
> especially when most of the time I’m working with networks that
> are /26 or smaller. I guess my big problem is confusion over labeling.
> What would be the equivalent of a /26, /27, /28 or have we done away
> with blocks that small and simply would just assign a /56 instead?
> 
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> 
> Does any of the gibberish I wrote make any sense at all?
> 
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> Any help anyone can offer is much appreciated.
> 
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> D -
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