netdev - Re: [PATCH] IPv6: Implement RFC 4429 Optimistic Duplicate Address Detection

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Date:	Fri, 26 Jan 2007 15:28:40 -0500
From:	Vlad Yasevich <vladislav.yasevich@...com>
To:	Neil Horman <nhorman@...driver.com>
Cc:	YOSHIFUJI Hideaki / 吉藤英明 
	<yoshfuji@...ux-ipv6.org>, sri@...ibm.com, davem@...emloft.net,
	kuznet@....inr.ac.ru, pekkas@...core.fi, jmorris@...ei.org,
	kaber@...eworks.de, netdev@...r.kernel.org
Subject: Re: [PATCH] IPv6: Implement RFC 4429 Optimistic Duplicate Address
 Detection

Hi Neil

Neil Horman wrote:
> On Fri, Jan 26, 2007 at 09:13:31AM +0900, YOSHIFUJI Hideaki / 吉藤英明 wrote:
>> In article <20070125194500.GB8891@...reliant.homelinux.net> (at Thu, 25 Jan 2007 14:45:00 -0500), Neil Horman <nhorman@...driver.com> says:
> 
> 
> New patch attached with most of your suggestions incorporated.  I've a few
> comments mixed in for some of the suggestions that I think need further
> discussion
> 
>> If optimistic_dad is disabled, flags should be IFA_F_TEMPORARY,
>> not IFA_F_TEMPORARY|IFA_F_OPTIMISTIC.
>>
>> Another idea is to use IFA_F_OPTIMISTIC not
>> IFA_F_OPTIMISTIC|IFA_F_TENTATIVE until the DAD has been finished.
>>
> 
> I'm currently setting the OPTIMISTIC flag in every location that its possibly
> needed, and then clearing it in addrconf_dad_start if that interface is not
> participating in optimistic dad.  I do this because the RFC in section 3.1
> indicates that manually configured addresses should not set the optimistic flag.
> If I removed the OPTIMISTIC flag from the locations it gets set in the patch and
> then only set it for participating interfaces in addrconf_dad_start, I would
> need to have some way to tell if the address in question was manually configured
> (to avoid setting it in that case).  At present I see no clear way to do that,
> but if you have a suggestion, I'll happily change this around.

One suggestiong/question:

Instead of clearing the OPTIMISTIC flag in addrconf_dad_start(), wouldn't it be better
to simply not set the flag in ipv6_add_addr()?  Just mask that flag from the 'flags'
argument passed to that function when conditions are right.

like 

if (!idev->cnf.optimistic_dad || ipv6_devconf.forwarding) 
	flags &= ~IFA_F_OPTIMISTIC;

The ifa->rt is also set there, so if the check for that is valid, we can do it there as well.

-vlad
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