netdev - Re: [PATCH net-next] net: ipv6/addrconf: make regen

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Date: Mon, 8 Jan 2024 11:52:53 -0700
From: David Ahern <dsahern@...nel.org>
To: Alex Henrie <alexhenrie24@...il.com>, netdev@...r.kernel.org,
 dan@...m.net, bagasdotme@...il.com, davem@...emloft.net,
 edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com, jikos@...nel.org
Subject: Re: [PATCH net-next] net: ipv6/addrconf: make regen_advance
 independent of retrans time

On 1/8/24 8:53 AM, Alex Henrie wrote:
> In RFC 4941, REGEN_ADVANCE is a constant value of 5 seconds, and the RFC
> does not permit the creation of temporary addresses with lifetimes
> shorter than that:
> 
>> When processing a Router Advertisement with a Prefix
>> Information option carrying a global scope prefix for the purposes of
>> address autoconfiguration (i.e., the A bit is set), the node MUST
>> perform the following steps:
> 
>> 5.  A temporary address is created only if this calculated Preferred
>>     Lifetime is greater than REGEN_ADVANCE time units.
> 
> Moreover, using a non-constant regen_advance has undesirable side
> effects. If regen_advance swelled above temp_prefered_lft,
> 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.
> 
> Some users want to change their IPv6 address as frequently as possible
> regardless of the RFC's arbitrary minimum lifetime. For the benefit of
> those users, add a regen_advance sysctl parameter that can be set to
> below or above 5 seconds.
> 
> Link: https://datatracker.ietf.org/doc/html/rfc4941#section-3.3
> Link: https://serverfault.com/a/1031168/310447
> Signed-off-by: Alex Henrie <alexhenrie24@...il.com>
> ---
>  Documentation/networking/ip-sysctl.rst | 20 +++++++++++++-------
>  include/linux/ipv6.h                   |  1 +
>  include/net/addrconf.h                 |  5 +++--
>  net/ipv6/addrconf.c                    | 17 +++++++++++------
>  4 files changed, 28 insertions(+), 15 deletions(-)
> 

net-next is closed; please repost in 2 weeks once it has re-opened.