In message <5A6D953473350C4B9995546AFE9939EE0B14C41E@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@isc.org