Subject: Re: [2.4 PATCH] bugfix: ARP respond on all devices

From: Daniel Gryniewicz <[email-masked]>
Date: 19 Aug 2003 15:12:43 -0400

I realize that, but is that a reason to keep linux from working with
these?  (And it's not just cisco, all the *BSDs (and therefore anything
that took the BSD stack such as MS) work this way too.)  As nearly as I
can tell, there's no way to make linux work with these, and the
situation I gave is one where linux could easily get it right, and
isn't.  Saying "They're broken.  Tough." is not really helpful.  At
least can we get a "work with broken other systems in certain
circumstances" switch somewhere?

(Funny you should mention Cisco, as we write routing software and must
interoperate with Cisco.  What Cisco says *does* go in the routing
community, if you wish your product to be used.  Currently, when our
customers come to us, we have to say "Either don't use Linux or run 2.2
with the arp fix patch.")

Daniel

On Tue, 2003-08-19 at 14:29, David S. Miller wrote:
> On 19 Aug 2003 14:30:26 -0400
> Daniel Gryniewicz <[email-masked]> wrote:
> 
> > If you are not on a shared lan, then it will *ONLY* work if linux is
> > on the other end.  No other system will work.
> 
> And these other systems are broken.  (actually, older Cisco equipment
> correctly responds to the ARP regardless of source IP)
> 
> Just because some Cisco engineer says that it is correct doesn't
> make it is.
> 
> Consider the situation logically.  When you're replying to an
> ARP, _HOW_ do you know what IP addresses are assigned to _MY_
> outgoing interfaces and _HOW_ do you know what subnets _EXIST_
> on the LAN?
> 
> The answer to both is, you'd don't know these things _EVEN_ if
> you are a router/gateway.
> 
> Therefore there is no valid reason not to respond to an ARP using one
> source address as opposed to another.
-- 
Daniel Gryniewicz <[email-masked]>