Are you talking about your basic ethernet address, or the
higher level (IP) addresses and configuration?

Devices generally store an ethernet address in a serial
EEPROM of some sort.  Once you have an ethernet address,
the rest of configuration is a well-examined problem:

> Have some sort of discovery program that runs as a PC
> application and allows you to configure the devices. Not
> a bad idea, but I can't program for PCs. Guess I'd have
> to find a partner. Also how to identify the individual
> units if they are geographically spread out?

Look into the "DHCP" Protocol imlpemntations (Dynamic Host
Configuration Protocol.)  This was aimed at configuring the
details of all those damn PCs clueless idiots kept connecting
to the corporate internet, and is well suited to getting a
pretty complete configuration for an arbitrary device starting
with nothing more than an ethernet address (and perhaps less,
for non-ethernet networks.)  Basically, when a host comes up
not knowing much about who it is, it sends a broadcast IP
packet to the DHCP server requesting information, and the
DHCP server responds with an IP address that can be used
by the device, the default router, the nameserver, ...,
and the name of config file that might contain additional
information of a less generic nature.

DHCP is built on top of the earlier BOOTP protocol.
BOOTP in turn addressed some of the limitations of
"Reverse ARP (RARP), which did nothing beyond assigning
an IP address based on ethernet address.

(now, a FULL implementation of everything in DHCP is going
to exceed the memory of most microcontrollers.  But a FULL
implementation is unlikely to be necessary...)

BillW
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