Subject: RE: A simple question

From: [email-masked]
Date: Tue, 22 Apr 2003 10:36:55 +0300

Hi Keith,

One comment:

> > Usage alters to meet the demands of the users.  That's nothing new.
> > 
> >   | on the contrary, having an enterprise use both SLs and globals creates
> >   | significant new problems of its own, and results in even less
> >   | flexibility than if SLs were used only by isolated networks.
> > 
> > Nothing that IPv4 doesn't have as well (if perhaps less commonly).
> 
> there's a reason that most v4 hosts don't have multiple addresses with varying
> scopes - it doesn't work well, and it creates problems for apps.  putting
> sitelocals in v6 is trying to impose those problems on all host.

I'd suggest that there has not been much of demand for this kind of
functionality. Most hosts have had only a single interface, so there is
not a lot of reason to give a single interface multiple addresses.

Already we are seeing laptops with multiple interfaces (Ethernet, WLAN,
Bluetooth, etc.) - I think it is only a matter of time that applications
start to take advantage of this.  

One use case for this kind of functionality would be a cell phone that
has some sort of expensive cellular data connnection but also has WLAN / 
Bluetooth interfaces. In a WLAN hotspot, data could/should go over that
interface as opposed to the cellular interface.  However, the cellular
interface might be used to provide WAN coverage ...

A lot of this is OS / implementation specific stuff, but I don't understand
why this should not be supported in standards.

br,
John

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From: "Stephen Sprunk" <[email-masked]>
Date: Tue, 22 Apr 2003 04:08:35 -0500

Thus spake <[email-masked]>
> Already we are seeing laptops with multiple interfaces (Ethernet,
> WLAN, Bluetooth, etc.) - I think it is only a matter of time that
> applications start to take advantage of this.

I see it as a failure of the network layer if applications need to
distinguish between multiple interfaces or address scopes.

While many don't see the distinction, this is the kind of stuff that
desperately needs to be in the OS/stack -- if anywhere.  Applications should
not know about network-level details unless they have a specific reason to
care, and if anything more than a small majority of applications care, there
is something wrong with our model.

Most applications today cannot even handle the case of multiple A records
for a destination host; do we really expect _tens of thousands_ of
applications to be updated with source-address-picking intelligence?

> why this should not be supported in standards.

The approach to other problems, such as QOS, is to provide a common
architecture and terminology, then let the individual vendors provide their
own (often creative) solutions within those confines.

S

Stephen Sprunk         "God does not play dice."  --Albert Einstein
CCIE #3723         "God is an inveterate gambler, and He throws the
K5SSS        dice at every possible opportunity." --Stephen Hawking