Re: mini-cores (was Re: ULA-C)

[Iljitsch van Beijnum <iljitsch at muada.com>]

On 20-sep-2007, at 14:52, Keith Moore wrote:

> > Well, a start would be a "connectbyname()" API call that takes  
> > care of
> > name-to-address mapping and trying different addresses until one  
> > works.

> Most IPv6-capable apps seem to implement that logic now.  And in my
> experience, it sucks.  Really hard.   The app can take a very long  
> time
> to establish a very poor connection.

If you're going to establish a poor connection, at least do it  
fast.  :-)

> The specific reason tends to be
> that the destination and source both have IPv4 and IPv6 addresses, and
> the IPv4 address works better than the IPv6 address (maybe because of
> 6to4 relay routers or whatnot), even though the v6 address is chosen
> first.

We can generalize this into: when you have a choice, you're going to  
make the wrong choice some of the time.

Downloading over IPv6 is still almost always slower than over IPv4,  
but for day-to-day stuff the performance difference isn't an issue  
with native IPv6 connectivity (for me). 6to4 is a crapshoot, it can  
be reasonable or it can completely fail, with everything in between.  
But it's never going to be better than native IPv4, obviously.

> But this is just an instance of the general case that some
> source-destination address pairs work better than others.  Address
> selection heuristics don't do a good job solving this problem - to  
> solve
> this problem the network actually needs to tell the host which
> source-destination address pairs will work well.  (and that's  
> pretty ugly)

I agree that this is an important issue, but I fail to see how this  
relates to applications knowing about addresses, unless applications  
are going to do their own performance testing, which I don't recommend.

> So what you seem to be doing is asking application writers to accept
> degraded performance and reliability in order to conform to some
> arbitrary notion of purity.   I don't see it happening.

Multiple addresses are a reality, not just because the IPv6 specs say  
so, but also because lots of hosts are going to have at least one  
IPv4 address and at least one IPv6 address. Has nothing to do with  
purity.

> On the other hand, if you make it such that application writers can  
> get
> good performance and reliability without messing with addresses, most
> won't see a need to bother with the complexity.  But there will  
> still be
> corner cases that will.

As I said, a good start would be that API because once applications  
use it, people working on better address selection etc have a place  
to insert their stuff and improve performance of real applications  
without having to rewrite the application.

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