Re: [B.A.T.M.A.N.] [PATCH] batman-adv: allow snooping gratuitous ARP Replies

["Linus Lüssing" <linus.luessing@c0d3.blue>]

On Fri, Feb 15, 2019 at 12:16:31AM +0800, Marek Lindner wrote:
> On Thursday, 14 February 2019 23:51:00 HKT Linus Lüssing wrote:
> > So far, gratuitous ARP Replies were ignored for DAT processing as it
> > contains a broadcast MAC address. This patch changes this and allows
> > snooping such ARP messages, too.
> 
> > Gratuitous ARP Replies were ignored since this commit:
> > ab361a9ccc5 ("batman-adv: filter ARP packets with invalid MAC addresses in 
> DAT")
> 
> You're kind enough to mention when the filter was introduced but fail to 
> explain why the filter introduced in the past was has outlived its usefulness 
> or how the new behavior addresses the  previous concerns.

That patch added filtering for both zero and broadcast MAC
addresses. While the original premise is correct - we do not want
those addresses in the DAT, the assumption that a broadcast MAC
address as ARP target MAC address were invalid, is wrong.
Gratuitous ARP Replies are valid packets.

So that patch was a bit too strict in that regard, I think. For
gratuitous ARP it's enough to ignore the (Target MAC/Target IP)
pair. Snooping the (Sender MAC/Sender IP) should be fine.