netdev - Re: [PATCH net] ip6_tunnel: fix GRE6 segmentation

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Message-ID: <20210624133915.GA4606@pc-32.home>
Date:   Thu, 24 Jun 2021 15:39:15 +0200
From:   Guillaume Nault <gnault@...hat.com>
To:     David Ahern <dsahern@...il.com>
Cc:     Jakub Kicinski <kuba@...nel.org>, davem@...emloft.net,
        netdev@...r.kernel.org, yoshfuji@...ux-ipv6.org,
        dsahern@...nel.org, vfedorenko@...ek.ru
Subject: Re: [PATCH net] ip6_tunnel: fix GRE6 segmentation

On Wed, Jun 23, 2021 at 12:28:05PM -0600, David Ahern wrote:
> On 6/23/21 10:14 AM, Jakub Kicinski wrote:
> > Noob question, why do we need that 2 sec wait with IPv6 sometimes?
> > I've seen it randomly in my local testing as well I wasn't sure if 
> > it's a bug or expected.
> 
> It is to let IPv6 DAD to complete otherwise the address will not be
> selected as a source address. That typically results in test failures.
> There are sysctl settings that can prevent the race and hence the need
> for the sleep.

But Jakub's script uses "nodad" in the "ip address add ..." commands.
Isn't that supposed to disable DAD entirely for the new address?
Why would it need an additional "sleep 2"?