Subject: RE: A Zeroconf situation?

From: "Christian Huitema" <[email-masked]>
Date: Wed, 29 Oct 2003 15:01:47 -0800

> Now, a static/DHCP IPv4 addressed device on the same broadcast domain
> wants
> to discover that type of device (or set of devices) in the domain, and
> configure them, in a uPnP sort of way, or maybe through a web browser.
I
> envision maybe a multicast address for discovery?

UPNP discovery is implemented using SSDP, which does indeed use
multicast. However, since you mention UPNP, you should consider this
excerpt from the UPNP architecture specification
(http://www.upnp.org/download/UPnPDA10_20000613.htm):

	The foundation for UPnP networking is IP addressing. 
	Each device must have a Dynamic Host Configuration 
	Protocol (DHCP) client and search for a DHCP server 
	when the device is first connected to the network. 
	If a DHCP server is available, i.e., the network is 
	managed, the device must use the IP addressed assigned 
	to it. If no DHCP server is available, i.e., the network 
	is unmanaged; the device must use automatic IP addressing 
	(Auto-IP) to obtain an address.

Auto-IP refers to the automatic address allocation protocol used in
versions of Windows since 98, i.e. the protocol that zeroconf is trying
to standardize. 

-- Christian Huitema

---

From: Stuart Cheshire <[email-masked]>
Date: Thu, 30 Oct 2003 17:28:26 -0800

>Effectively,  we have two ships-in-the-night V4 subnets on a broadcast
>domain.  Most V4 stacks won't have a link local and globally scoped address
>on the same interface.  Even if I multicast from a non v4LL address to a
>v4LL address, how would the v4LL device be able to respond to an 'off
>subnet' address (apparently, it wouldn't?)
>
>So in short, is there a
>
>1) Means to communicate between a link local and globally scoped address?
>Is it allowed?
>2) Means to discover the device(s) that have a Link Local address?

Communication between the link-local and routable subnets on the same 
physical link is allowed, encouraged, and described in

<http://www.zeroconf.org/Rendezvous/#RTLL>

>The fundamenal idea is that I can drop an unconfigured device onto any
>network in a non-disruptive way, and then discover and configure it while
>not having to mess with the stack/addressing of the configuring machine.
>
>Is this problem addressed?

Yes, this is an important issue. When Apple shipped the first AirPort 
base station all those years ago, the ability to configure it without 
having to change the network settings on the client machine was very 
important, and this is why we added route-to-link-local in OS 9, and then 
later in OS X when OS X launched.

Stuart Cheshire <[email-masked]>
 * Wizard Without Portfolio, Apple Computer, Inc.
 * www.stuartcheshire.org