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Re: Restrict local IP announcements in ARP requests

To: Julian Anastasov <ja@xxxxxx>
Subject: Re: Restrict local IP announcements in ARP requests
From: "David S. Miller" <davem@xxxxxxxxxx>
Date: Wed, 11 Feb 2004 20:16:56 -0800
Cc: netdev@xxxxxxxxxxx, linux-net@xxxxxxxxxxxxxxx
In-reply-to: <Pine.LNX.4.58.0402100251380.1251@u.domain.uli>
References: <Pine.LNX.4.58.0402081149001.6268@u.domain.uli> <20040209140853.69ab8bea.davem@redhat.com> <Pine.LNX.4.58.0402100049470.1251@u.domain.uli> <20040209151053.1f63937a.davem@redhat.com> <Pine.LNX.4.58.0402100251380.1251@u.domain.uli>
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On Tue, 10 Feb 2004 03:00:24 +0200 (EET)
Julian Anastasov <ja@xxxxxx> 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.

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