Date: Thu, 22 Sep 2016 08:41:44 -0700 From: Gleb Smirnoff <glebius@FreeBSD.org> To: Steven Hartland <killing@multiplay.co.uk> Cc: Ryan Stone <rysto32@gmail.com>, Kubilay Kocak <koobs@freebsd.org>, freebsd-net <freebsd-net@freebsd.org>, Karl Pielorz <kpielorz_lst@tdx.co.uk> Subject: Re: lagg Interfaces - don't do Gratuitous ARP? Message-ID: <20160922154144.GO1018@cell.glebi.us> In-Reply-To: <f4100561-4977-0b19-c245-0cd09438943d@multiplay.co.uk> References: <0D84203FAAFD0A8E7BBB24A3@10.12.30.106> <bc33560b-59bc-01be-6a5d-7994ac121258@multiplay.co.uk> <6E574F1B61786E6032824A88@10.12.30.106> <2c62f5f0-3fb4-f513-2a8f-02de3a1d552f@FreeBSD.org> <20160921235703.GG1018@cell.glebi.us> <CAFMmRNwZBEJ9Me4FSh=W7fRNjm4344jiUGuJqX8KUB_0sWcajA@mail.gmail.com> <20160922025856.GH1018@cell.glebi.us> <348d534d-ef87-f90c-aa43-cc65c2f6283c@multiplay.co.uk> <20160922150940.GK1018@cell.glebi.us> <f4100561-4977-0b19-c245-0cd09438943d@multiplay.co.uk>
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On Thu, Sep 22, 2016 at 04:34:03PM +0100, Steven Hartland wrote: S> On 22/09/2016 16:09, Gleb Smirnoff wrote: S> > On Thu, Sep 22, 2016 at 08:21:08AM +0100, Steven Hartland wrote: S> > S> On 22/09/2016 03:58, Gleb Smirnoff wrote: S> > S> > On Wed, Sep 21, 2016 at 09:12:11PM -0400, Ryan Stone wrote: S> > S> > R> > IMHO, the original patch was absolutely evil hack touching multiple S> > S> > R> > layers, for the sake of a very special problem. S> > S> > R> > S> > S> > R> > I think, that in order to kick forwarding table on switches, lagg S> > S> > R> > should: S> > S> > R> > S> > S> > R> > - allocate an mbuf itself S> > S> > R> > - set its source hardware address to its own S> > S> > R> > - set destination hardware to broadcast S> > S> > R> > - put some payload in there, to make packet of valid size. Why should it be S> > S> > R> > gratuitous ARP? A machine can be running IPv6 only, or may even use S> > S> > R> > whatever S> > S> > R> > higher level protocol, e.g. PPPoE. We shouldn't involve IP into this S> > S> > R> > Layer 2 S> > S> > R> > problem at all. S> > S> > R> > - Finally, send the prepared mbuf down the lagg member(s). S> > S> > R> > S> > S> > R> > And please don't hack half of the network stack to achieve that :) S> > S> > R> S> > S> > R> The original report in this thread is about a system where it takes almost S> > S> > R> 15 minutes for the network to start working again after a failover. That S> > S> > R> does not sound to me like a switch problem. That sounds to me like the ARP S> > S> > R> cache on the remote system. To fix such a case we have to touch L3. S> > S> > S> > S> > Does lagg(4) hardware address change when it failovers? S> > S> > S> > S> It moves the address between interfaces which typically moves it between S> > S> switches too. S> > S> > So, the address doesn't change, which means ARP cache doesn't need to S> > change as well. If it moves between switches, all that needs to be done S> > is to send whatever packet from proper hardware address to broadcast. S> > S> That would be nice but unfortunately in the wild that won't work as S> without GARP devices can and do ignore :( You can create a fake gratious ARP packet, if you want. Switches must not require IP addresses matching the reality in the packet. P.S. I always read GARP as Generic Attribute Registration Protocol. -- Totus tuus, Glebius.
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