From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 22DBA17CD for ; Thu, 26 Oct 2023 00:43:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="TyjT9evM" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2AA06C433C7; Thu, 26 Oct 2023 00:43:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1698281003; bh=o74fcJsVBea/xhgwWVCnWC14swdPhGAlQdOGJ04AzI4=; h=Date:Subject:To:References:From:In-Reply-To:From; b=TyjT9evMpsPFRFfzb5PgixLSm8WTkxS+Jb/C3W4ADVaY4boC57WaLcwaFLdsPD92c UDoctDZpUpM9jAtAXPVXJq60Fr9LxPGhKLdsfVSj8IdeDo8En5GYP1GdnbvquJ3QQw Y10+JwjLqo+Qwz6ZQ0c1JKrR9TuehA46yAJfu/bjVOKD3zNNhHWChaKQ0dnY8JcuTi wlL/kbAbmRYAhPsXvyOpn38e9093uZTE61/GSqUFMeji2slo7olfeJ6t9WScfcIt8i a8iU6e5bVuywA/YWVPzynFHFD5qWffY0THmz716qbtdsSHsvdfQKhq++dV8EdR3MY4 UlBrki3wTas4w== Message-ID: <862dc7d4-d5a3-4a17-984b-d3dcc1015e61@kernel.org> Date: Wed, 25 Oct 2023 18:43:22 -0600 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH net-next v2 2/4] net: ipv6/addrconf: clamp preferred_lft to the minimum required Content-Language: en-US To: Alex Henrie , netdev@vger.kernel.org, jbohac@suse.cz, benoit.boissinot@ens-lyon.org, davem@davemloft.net, hideaki.yoshifuji@miraclelinux.com, pabeni@redhat.com, kuba@kernel.org References: <20231024212312.299370-1-alexhenrie24@gmail.com> <20231024212312.299370-3-alexhenrie24@gmail.com> From: David Ahern In-Reply-To: <20231024212312.299370-3-alexhenrie24@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/24/23 3:23 PM, Alex Henrie wrote: > If the preferred lifetime was less than the minimum required lifetime, > ipv6_create_tempaddr would error out without creating any new address. > On my machine and network, this error happened immediately with the > preferred lifetime set to 1 second, after a few minutes with the > preferred lifetime set to 4 seconds, and not at all with the preferred > lifetime set to 5 seconds. During my investigation, I found a Stack > Exchange post from another person who seems to have had the same > problem: They stopped getting new addresses if they lowered the > preferred lifetime below 3 seconds, and they didn't really know why. > > The preferred lifetime is a preference, not a hard requirement. The > kernel does not strictly forbid new connections on a deprecated address, > nor does it guarantee that the address will be disposed of the instant > its total valid lifetime expires. So rather than disable IPv6 privacy > extensions altogether if the minimum required lifetime swells above the > preferred lifetime, it is more in keeping with the user's intent to > increase the temporary address's lifetime to the minimum necessary for > the current network conditions. > > With these fixes, setting the preferred lifetime to 3 or 4 seconds "just > works" because the extra fraction of a second is practically > unnoticeable. It's even possible to reduce the time before deprecation > to 1 or 2 seconds by also disabling duplicate address detection (setting > /proc/sys/net/ipv6/conf/*/dad_transmits to 0). I realize that that is a > pretty niche use case, but I know at least one person who would gladly > sacrifice performance and convenience to be sure that they are getting > the maximum possible level of privacy. > > Link: https://serverfault.com/a/1031168/310447 > Signed-off-by: Alex Henrie > --- > net/ipv6/addrconf.c | 18 +++++++++++++----- > 1 file changed, 13 insertions(+), 5 deletions(-) > Reviewed-by: David Ahern