Re: [Sheflug] Slightly OT: Configuring IP addresses

[nospam [at] alexhudson.com]

Just as a slight aside, what are the actual 'specs' for this feature?
Getting MAC information is highly reliable on the local topology - you're
not guaranteed to be able to get it, even if you're on the same switch
(although fairly unlikely). MACs can be blocked (often are - VLAN),
'masqueraded', all sorts. You're probably not going to see stuff from other
subnets, or even the same subnet (again, depending on what's in the way).

This is why DHCP/bootp (sort of) works - you listen to a broadcast IP
address (255.255.255.255 in this instance) to negotiate for an ip address
without treading on others' toes. That's the best option, but again,
crossing switches can be tough - it requires proper routing. Some switches
won't let it through full stop (depending on firmware). The other option is
to write your own protocol, based on a fixed known IP, or a multicast IP,
and do it that way. Not very hard, but not necessarily as flexible.

Perhaps the best way is to assign one unit as 'master'. This gets a fixed ip
from the serial port interface (i.e., plug a laptop into it). It would then
dole out IP addresses via dhcp to 'slaves' on the local subnet. That way,
configuration for the slaves can be changed via the master, which would be
far more accessible than some MAC/ping madness... but, it depends on whether
or not you think this is going to be installed on simple, or complex,
topology...

Cheers,

Alex.

On Fri, Apr 06, 2001 at 12:39:53PM +0100, wulfie wrote:
> Look at ARP/RARP.... you can access the MAC address & set up an IP address
> over the Lan.
> 
> > We are currently developing a system that uses an embeded controller card
> > and has an ethernet port. When the product is shipped we want to be able
> to
> > give the customer means of setting / changing the IP address. 

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