Re: Proxy ARP

[Ryota Ozaki <ozaki-r%netbsd.org@localhost>]

On Tue, Mar 8, 2016 at 12:36 AM, Robert Elz <kre%munnari.oz.au@localhost> wrote:
>     Date:        Mon, 7 Mar 2016 19:43:58 +0900
>     From:        Ryota Ozaki <ozaki-r%netbsd.org@localhost>
>     Message-ID:  <CAKrYomi9fEaC5BO64Rw==jujXPZaMJQXmVc=U=HX-wtyrZw8VQ%mail.gmail.com@localhost>
>
>   | I agree proxy ARP can be used that case and we can do so with NetBSD,
>   | but in that case we also have to set up a machine to receive frames
>   | that have the destination of someone's MAC address....
>
> No, that was never the method, and should not be necessary ever when
> using arp (there are other use cases for things like that.)   The idea
> was just to provide an arp service that announced someone else's MAC
> address, once the node making the ARP query received that info it would
> send later packets to the MAC address it was told - for which there should
> be a system on the net to receive those frames (we do not relay them). It
> was used when that other (destination) host simply did not understand ARP,
> but otherwise could handle IP just fine.

Oh, I see. I didn't image that...

>
>   | Anyway I'm not sure NetBSD's proxy ARP is intended for the case
>
> In the early days, BSD ARP was most certainly used for that, and NetBSD
> comes from that ancestry, and most likely has  remnants of code for that
> purpose left in it - whether it still works or not is a different question.
>
>   | and there are users for it.
>
> There might easily be none, as I said, I really cannot imagine a real
> host left working these days that supports IP and not ARP, it would have
> to be truly ancient and running truly ancient code.

Agreed.

>
> Cases where the host answering the ARP actually wants to receive the
> packets to then relay to some other host (whether out some p2p link, or
> to a virtual host on the same system makes no difference for this) are
> much more common, and much more likely to remain relevant today.

I wrote some tests for the case using tap. I hope the tests are applicable
to p2p links.

  ozaki-r

>
> Certainly the integration of ARP into the routing table is (relatively) new,
> when the first case above was in actual use, it was not implemented that way.
>
> kre
>