Re: Linux 2.2 - BSD/OS 4.1 ARP incompatibility

From: Andrey Savochkin (saw@saw.sw.com.sg)
Date: Mon Sep 04 2000 - 04:47:00 EST


On Mon, Sep 04, 2000 at 11:22:31AM +0200, Andi Kleen wrote:
> On Mon, Sep 04, 2000 at 05:06:15PM +0800, Andrey Savochkin wrote:
> > So, I think that we have to be sure that we use the "best" address for this
> > destination.
> > What about an unconditional use of inet_select_addr() or fib_select_addr()
> > based on prefsrc with inet_select_addr() fallback?
>
> It looks fine in theory, but I'm sure it'll break with some anal ARP filters.
> (so at least for 2.2 we probably would need to sysctl it, or teach lots
> of users about prefsrc)

When it comes to "hidden" interfaces, I don't expect problems because this
change makes them even more "hidden".

> I guess Alexey would hate your implementation because it adds a
> unnecessary fib_lookup() in a reasonable fast path, it would probably be
> better to cache it in the dst entry and pass it in.

That's a good argument against.
Let's wait for the actual Alexey's complaint :-)
I would place the cached source into neighbor structure, if it matters.
However, I'm not sure if arp requests are so frequent events.
Once in 20 seconds per neighbor...

        Andrey
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