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Date:      Sat, 9 Oct 1999 16:14:33 -0500 (CDT)
From:      Mohit Aron <aron@cs.rice.edu>
To:        julian@whistle.com (Julian Elischer)
Cc:        sthaug@nethelp.no, freebsd-net@freebsd.org, justin@apple.com, alc@cs.rice.edu, wollman@khavrinen.lcs.mit.edu
Subject:   Re: arp errors on machines with two interfaces
Message-ID:  <199910092114.QAA11499@cs.rice.edu>
In-Reply-To: <Pine.BSF.4.05.9910091356490.53621-100000@home.elischer.org> from "Julian Elischer" at Oct 9, 99 02:06:54 pm

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> Why are you doing this? 
> Why not just assign the two addresses to the same
> NIC? (though I guess with a switch you may be able to get twice the
> throughput with two NICs..)
> 

Actually I do have aliases on each of the interfaces but as you guessed, 
the two interfaces are there to get more throughput. The machine has a
500 MHz Pentium III processor (actually 4 of them, but I'm just using one for
now). Its not possible to saturate the machine with just one 100Mbps interface.
I need to have multiple interfaces.


> He does have a point however.. ARP packets that are not for the networks
> that are on teh receiving NIC could probably be safely discarded without
> effecting the way that the system supports the spec. I think it's vague on
> this point, and we SEE that other people do similar. I would actually
> thinkmthat it would be a security imporovement.
> I don't think we should accept cofiguration or routing information from
> machines that are not on the right network.
> 
> If I had one net inside a firewall and one outside, I don't want to
> recieve ARP packets from the outside that are influencing my internal
> routint (arp) table.
> 
> This is not that unsupported.. High availability hosts do this all the
> time, and need to.
> 
> My suggestion is that we check incoming arp packets  to discard
> packets that resolve addresses that are not in a netrange on the interface
> into which they came.
> 
> I think this is a good idea anyway for security reasons and we can
> dispense with the check against ALL local networks. It might even be
> faster.
> 


Thanks for clarifying the specs and supporting my suggestion. I do really 
need this configuration and all high end server systems that I know use it too.



- Mohit


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