netdev - Re: [PATCH] bonding: send IPv6 neighbor advertisement on failover

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Message-ID: <48ED03A6.2060705@hp.com>
Date:	Wed, 08 Oct 2008 15:01:58 -0400
From:	Brian Haley <brian.haley@...com>
To:	David Stevens <dlstevens@...ibm.com>
CC:	Alex Sidorenko <alexandre.sidorenko@...com>,
	David Miller <davem@...emloft.net>, fubar@...ux.vnet.ibm.com,
	Simon Horman <horms@...ge.net.au>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	netdev-owner@...r.kernel.org,
	Vladislav Yasevich <vladislav.yasevich@...com>
Subject: Re: [PATCH] bonding: send IPv6 neighbor advertisement on failover

David Stevens wrote:
> Well, actually, it looks like I'm suggesting you to re-use something that 
> doesn't
> exist. :-)
> 
> MLD (and IGMP) has such a thing where unsolicited advertisements are sent
> multiple times, with delays in between, to account for lossy networks 
> possibly
> dropping the first one. There are configurable counts associated with 
> probes
> and retransmit intervals for solicits, but I don't see the equivalent yet 
> for
> unsolicited NA's.

I don't see an equivalent either, since the only unsolicited NA the 
kernel sends is for DAD, which uses dad_transmits.

I left the MLD changes out of this patch so I could work on it 
separately, when I get to it I'll make sure to look at the issues you 
raised in your other email so it follows the RFC, or at least the Linux 
behavior.

> So, instead, what I suggest is that you add (or find!) THAT knob, instead 
> of a
> bonding-specific one. Because adding an address that wasn't there before
> has identical issues with unsolicited NA's as bonding has with activating 
> a
> new address. The default should probably be 1, but if you ever need to
> send multiple unsolicited NA's for bonding, you probably also need it for
> adding a normal address on the same network. dad_transmits is similar,
> but not really the same thing.

The problem is that dad_transmits can be set to zero, although not 
recommended, so if we used that value then bonding failover would be 
just as broken.  I think having this new tunable stay in the bonding 
code is useful since that's the code that's actually doing the transmit.

-Brian
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