[ale] OT: device discovery

[Greg Freemyer]

Not quite sure what your asking.

You could consider setting up a class-D multicast address on all of
your to be discovered devices.  (ie. Every device would have the same
multicast IP address in addition to its normal IP)  One negative is
that most routers, etc. don't pass multicast by default, but if you
only have one lan segment I think it should work.

See http://en.wikipedia.org/wiki/Multicast_address

If you go this way, then your discovering device would send out the
multicast message with its IP in it.  Your to be discovered device
would be listening for the multicast message.  When it got it, it
would pull out the senders IP and open up a new socket back to it
using its standard IP address.

You can either get an officially assigned class-D IP.  (Unique to your
devices across the Internet.)

Or if that is not reasonable:

"Potential conflicts with Internet multicast address assignments can
be avoided by using GLOP addressing (AS required) or administratively
scoped addresses. Such addresses can be safely used on a network
connected to the Internet without fear of conflict with multicast
sources originating on the Internet. Administratively scoped addresses
are roughly analogous to the unicast address space for private
internets. Site-local multicast addresses are of the form 239.255.x.y,
but can grow down to 239.252.x.y if needed. Organization-local
multicast addresses are of the form 239.192-251.x.y, but can grow down
to 239.x.y.z if needed."

Greg

On 12/1/06, David Hamm <ale at spinnerdog.com> wrote:
> Hi,
>
> I have a device that runs Linux and is to be delivered into environments that
> have little or no technical resources, DHCP may not be running either so I
> need a way of "discovering" the device regardless of it's IP address.
>
> One technique is to maintain an alias on the interface (IE 172.16.*.*) and
> temporarily ad an alias to the system on which the "discovery" will be run.
>
> Can anyone suggest a more elegant method?
>
> Ideally the "discovery" application would allways find the device, obtain it's
> IP address and take the necessary steps to establish communications.
>
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> Ale at ale.org
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>


-- 
Greg Freemyer
The Norcross Group
Forensics for the 21st Century