IPv6 fc00::/7 — Unique local addresses

Thu Oct 21 02:22:24 UTC 2010

In message <4CBF9B7A.1000500 at matthew.at>, Matthew Kaufman writes:
> On 10/20/2010 6:20 PM, Mark Smith wrote:
> >
> > To make it clear, as it seems to be quite misunderstood, you'd have
> > both ULA and global addressing in your network.
> 
> Right. Just like to multihome with IPv6 you would have both PA addresses 
> from provider #1 and PA addresses from provider #2 in your network.
> 
> Only nobody wants to do that either.

Only because there isn't good support for it yet.

ULA + PA actually works today.  The IP stack can do the address
selection without worrying about reachability.  The chances of the
ULA being unreachable and the PA being reachable between two nodes
in the same ULA prefix are negligable.  If I'm talking to a ULA
address I'll use my ULA address.  If I'm talking to a non-ULA address
I'll use my PA addresses.

PA + PA is a problem because you need to worry about source address
selection and that is driven by reachability.  You also need to
worry about egress points due to source address filtering. etc.

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