Re: IPv6 fc00::/7 — Unique local addresses

Thu Oct 21 11:33:37 UTC 2010

For for all intents and purposes if you're looking for RFC1918 style
space in IPv6 you should consider the block FD00::/8 not FC00::/7 as
the FC00::/8 space is reserved in ULA for assignment by a central
authority (who knows why, but with that much address space nobody
really cares).

People may throw a fit at this, but as far as I'm concerned FD00::/8
will never leave the edge of our network (we null route ULA space
before it can leak out, just like you would with RFC1918 space).  So
you can pretty much use it has you see fit.  If you want to keep your
ULA space short there is nothing stopping you from using something
like FD00::1 as a valid address.

You could embed your ASN into it or some other identifier if you want
to avoid conflicts with other non-routed address space which should
never enter or leave your network from the outside, but I'm just not
seeing the practical application for this.

On Wed, Oct 20, 2010 at 5:48 PM, Jeroen van Aart <jeroen at mompl.net> wrote:
> <IPv6 newbie>
>
> According to http://en.wikipedia.org/wiki/IPv6_address#Special_addresses an
> fc00::/7 address includes a 40-bit pseudo random number:
>
> "fc00::/7 — Unique local addresses (ULA's) are intended for local
> communication. They are routable only within a set of cooperating sites
> (analogous to the private address ranges 10/8, 172.16/12, and 192.168/16 of
> IPv4).[12] The addresses include a 40-bit pseudorandom number in the routing
> prefix intended to minimize the risk of conflicts if sites merge or packets
> are misrouted into the Internet. Despite the restricted, local usage of
> these addresses, their address scope is global, i.e. they are expected to be
> globally unique."
>
> I am trying to set up a local IPv6 network and am curious why all the
> examples I come accross do not seem to use the 40-bit pseudorandom number?
> What should I do? Use something like fd00::1234, or incorporate something
> like the interface's MAC address into the address? It'd make the address
> quite unreadable though.
>
> Thanks,
> Jeroen
>
> --
> http://goldmark.org/jeff/stupid-disclaimers/
> http://linuxmafia.com/~rick/faq/plural-of-virus.html
>
>

-- 
Ray Soucy

Epic Communications Specialist

Phone: +1 (207) 561-3526

Networkmaine, a Unit of the University of Maine System
http://www.networkmaine.net/