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

[Matthew Kaufman <matthew () matthew at>]

On 10/20/2010 7:22 PM, Mark Andrews wrote:
> In message<4CBF9B7A.1000500 () 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.
Too bad that support didn't come first, or all the issues with address 
allocation and routing table size being discussed elsewhere wouldn't be 
a problem for operators.
> 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.
ULA + PA can have the same problems, especially if your ULA is 
inter-organization ULA, which was one of the cases under discussion.

Matthew Kaufman