Subject: Re: Restrict local IP announcements in ARP requests

From: "David S. Miller" <[email-masked]>
Date: Wed, 11 Feb 2004 20:16:56 -0800

On Tue, 10 Feb 2004 03:00:24 +0200 (EET)
Julian Anastasov <[email-masked]> wrote:

> 	If you like it in this way you can apply now or after
> some days or to delay it if we want to combine it with other
> device flags or changes.

I like the patch, but I want the documentation changed.

If you'll recall, one of the big problems Alexey and myself
had with the new ARP saddr selection behavior you propose is
that it assumes that: if we do not know of a certain subnet
being on a link than this subnet does not exist there.

In some environments this assumption holds.  But "some != all"
as I often say to a friend of mine :-)

No router has this knowledge completely, and in many environments
such an assumption does not hold.

I know you understand this, which is why your patch keeps the
current behavior the default.

But I want the docs for the sysctl to talk about this.  Something
simple like:

+	1 - Try to avoid local addresses that are not in the target's
+	subnet for this interface as far as we know.  In some environments
+	subnets may be active that this system is not aware of, thus this
+	setting might cause problems in such cases.

Tweak it however you wish, just get the idea/warning across.

I'd also prefer if you at least lightly define what "best" source address
means in the context of arp_announce==2.

Thanks.