[Novalug] IPV6 name lengths

Bryan J Smith b.j.smith@ieee.org
Sun Jul 12 13:46:06 EDT 2015


First off, you're confusing DNS with IPv6 Addresses.

Secondly, IPv6 Addressses are 128-bits, but only 64-bits are actually
assigned a part of the system.  And there are at least three (3)
different ones that everyone _must_ know of.

So ... let's get the "Interface Identifier" out of the way, the
"right" 64-bits (which is not technically accurate, but I'll use it).
It is in Extended Unique Identifier (EUI-64) format, designed to be
[nearly] universally unique, often based on the 48-bit MAC address, or
other hardware address (if not MAC-48).

This leaves the "left" 64-bits of the "Prefix."  The first 48-bit is
known as the "Routing Prefix" and the last 16-bit is known as the
"Subnet ID."

The first 48-bit will start with a known prefix in many cases,
sometimes as short as 8-bit, other times 10 to 12 or even 16-bits,
using 2-8 bits to differentiate the "type" of subprefix.  This seems
confusing at first, but you'll quickly understand why.  E.g., why
you'll see things like fe80::/10 and fd00::/8 most often -- the first
16-bits of the prefix, even if the CIDR says 8 or 10, meaning you can
only consider the first 8 or 10 bits (and possibly ignore the zeros
after, as they may be non-zeros in a real address).

That said, when it comes to IPv6 "Prefixes" for unicast/anycast
(ignoring multicast), everyone _must_ know the following ...

Link Local Address
- fe80::/10, always fe80::/64 - local net, non-routable [A]
- 10-bit prefix + 54-bit = 64-bit Prefix (all zeros, non-routable)
- Direct equivalent to IPv4 169.254/16 (again, non-routable)

Unique Local Address (ULA) [B]
- fd00::/8 [C], per org fdxx:xxxx:xxxx:/48 for org, fd:(prior
xxxx):yyyy:/64 for each subnet
- 8-bit prefix + 40-bit Global ID (random) + 16-bit Subnet ID
(non-Internet routable)
- Pseudo-equivalent to IPv4 10/8, 172.16/12 and 192.168/16 (private,
non-Internet routable)
- The 16-bit allows the creation of 65,536 networks internal to the organization
- The 40-bit Global ID is pseudo-random for the organization
- The Global ID is generated with a suggested date/timestamp "seed" algorithm

Global Unicast Addresses
- 2000::/3 - Assigned by IANA [1]
- 3-bit prefix + variable (assigned to region) + variable (left to be
assigned by region)
- IANA has typically assigned using 9 to 20-bit (::/12 to ::/23) to
regional authorities
- Regions are free to do as they wish, but it is recommended they assign /48
So ...
- /48 = 3-bit prefix + 9 to 20 (IANA assigned) + 25 to 36 (region assigned)
Ergo ...
- IANA assigns from 512 (/12) to 1M (/23) prefixes to regions, so ...
- Region assigns from 32M to 64B (/48) prefixes to entities, so ...
- Assigning entities assign 64K Subnets (/64) as they see fit, so ...
Furthermore ...
- Assigning entities are encouraged to assign /56 to organizations, so ...
- Assigning entities can assign up to 256 (/56) prefixes so an
organization can self-assign 256 Subnets (/64)

If you're not seeing the brilliance of the 48-bit "Routing Prefix" ...
- It's kinda like a Class A ... say with an ISP
- Allowing it to be broken up into 256 Class Bs ... say for 256 companies
- Which can break them up into 256 Class Cs ... for 256 of their own subnets
- Only with IPv6, instead of having only 256 addresses, there's the full EUI-64

That's basically how it all works.

-- bjs

[1] IANA -- Current IPv6 Unicast Address Assignments
- http://www.iana.org/assignments/ipv6-unicast-address-assignments/ipv6-unicast-address-assignments.xhtml

[A] When one sees "::" it means "all zeros between the colons."  E.g.,
fe80::/64 = fe80:0000:0000:0000:

[B] ULA was not the original design for private networks.  There was
to be a Site Local Address (SLA) that everyone had to register, to
prevent conflicts.  Unfortunately most entities considered this to be
a security issue, having their "Network

[C] ULA is actually reserved fc00::/7, but fc00::/8 itself is reserved
for future use, with fd00::/8 being for ULA as documented here.



On Sun, Jul 12, 2015 at 8:55 AM, Walt Smith via Novalug
<novalug@firemountain.net> wrote:
> HI,
> Just wondering, for the sake of wondering...
> IPV6 has, what, 256 bits ?  divided into 4 groups,
> only one of which should last (be) longer than the universe ?
> OK, its those 256 bits, errrr, 64 hex digits.
> Or is it 256 hex digits ?
>
> Q:
> How many meaningful ASCII chars can the IPV6
> represent, rather, from the human side, how long a string
> will it be * necessary* to use ina  few years when we
> use up DNS names like
> https://MyColonIstheBiggestInTheWorldAndYoursIsNot.com
> ?
>
> I guess this will eventually include Chinese/Japanese/Korean
> chars outside the U.S. and might include of, but not all of the IoT.
> and not subdirs.  /this /that/doh/filename  (I suppose Alibaba's kittys
> collar IP might have an IP.  Will ID bracelets get small enough
> for pet cockroaches ?  What about #8 bolt number at Home Depot ?)
>
> Q repeated:
> Has any study been done on domain name char lengths upcoming
> in the next decades ???
>
> U Think I'm worrying too much ?



More information about the Novalug mailing list