RE: [2.4 PATCH] bugfix: ARP respond on all devices

David S. Miller wrote: 

quoted

	IP packets you mean? You don't? ;) It would depend on why you're
doing it naturally. Mostly, I'd have thought that if a host 

doesn't have an

quoted

IP number it doesn't get to use ARP.

Of course it gets to use ARP, nothing prevents this.

If I know that IP X has my configuration information, I
have every right to send X a packet from zero-net to
ask for that information before I have any IP addresses
attached to the interface.

	Ick! And how is IP X going to get the information back? Broadcast
it, too? Here was me thinking that protocols like BOOTP and DHCP were
appropriate for this.

	If you are going to send from 0.0.0.0, then I assume there's
something in the ARP standard to say "don't cache this ARP request" - I must
have missed it. If so, that's a special case - no need to spoil things
elsewhere, though.

Also, when one specifies a specific device in an output
address and we cannot find the IP part of the address
in the routing tables, we still procure a valid route for
the requester.

	Well, what do you do currently? If the packet you're routeing came
from another host, there's no way in hell you can use their IP address in an
ARP request ... is there? I certainly hope you don't go that far!!!

	If it's a locally generated packet, then the next hop must be on the
same subnet as the address it's coming from - there's your IP number.

Besides normal IP addresses, multicast tools use these
facilities.

	Multicast uses ARP? That's news to me!

		Richard

On Tue, 19 Aug 2003 20:00:44 +0100
Richard Underwood [off-list ref] wrote:

David S. Miller wrote: 

quoted

If I know that IP X has my configuration information, I
have every right to send X a packet from zero-net to
ask for that information before I have any IP addresses
attached to the interface.

	Ick! And how is IP X going to get the information back?

It knows the MAC address of the intended receiver, there is
no problem here.

	If you are going to send from 0.0.0.0, then I assume there's
something in the ARP standard to say "don't cache this ARP request" - I must
have missed it. If so, that's a special case - no need to spoil things
elsewhere, though.

What is the caching problem?  The ARP response is valid, and we
have no reason to believe otherwise.

	Well, what do you do currently? If the packet you're routeing came
from another host, there's no way in hell you can use their IP address in an
ARP request ... is there? I certainly hope you don't go that far!!!

We're not talking about routing scenerios, we're talking strictly
about packets being originated by an application on the local host.

quoted

Besides normal IP addresses, multicast tools use these
facilities.

	Multicast uses ARP? That's news to me!

It uses routes that only have been determined only using the desired
device index.  There is no "interface address" to match up to when
we're trying to send to a multicast address.