IPv6 fc00::/7 - Unique local addresses

Fri Oct 22 00:33:12 UTC 2010

In message <5A6D953473350C4B9995546AFE9939EE0B14C41E at RWC-EX1.corp.seven.com>, "
George Bonser" writes:
> > Sent: Thursday, October 21, 2010 3:16 PM
> > To: Owen DeLong
> > Cc: NANOG list
> > Subject: Re: Re: IPv6 fc00::/7 - Unique local addresses
> >=20
> > IPv4 think.
> >=20
> > You don't re-address you add a new address to every node.  IPv6 is
> > designed for multiple addresses.
> >=20
> 
> How does your application on the host decide which address to use when
> sourcing an outbound connection if you have two different subnets that
> are globally routable?

But ULAs aren't globally routable.  ULA addresses are easy to
identify and guess what IPv6 stacks know how to select different
source address depending apon the destination address.  They also
know how to order the addresses returned to the application such
that reachable ULA's are returned first and non-reachable ULAs are
returned last.

You can do the same thing with a RIR assigned prefix for internal
communication but it requires more explict configuration.  With
ULA's the IPv6 stack can auto configure itself as you have a well
known identifier.

Any node that supports RFC3484 (February 2003) can do this for you
though you may need to override the defaults.  If your OS doesn't
yet support it complain.  The ability to set this site wide is also
coming.

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