netdev - Re: [PATCH net-next 1/2] tcp: remove per-destination timestamp cache

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Message-ID: <20170315225508.GB14761@1wt.eu>
Date:   Wed, 15 Mar 2017 23:55:08 +0100
From:   Willy Tarreau <w@....eu>
To:     David Miller <davem@...emloft.net>
Cc:     soheil.kdev@...il.com, netdev@...r.kernel.org, soheil@...gle.com,
        edumazet@...gle.com, ncardwell@...gle.com, ycheng@...gle.com,
        lvml@....de, fw@...len.de
Subject: Re: [PATCH net-next 1/2] tcp: remove per-destination timestamp cache

Hi David,

On Wed, Mar 15, 2017 at 03:40:44PM -0700, David Miller wrote:
> From: Soheil Hassas Yeganeh <soheil.kdev@...il.com>
> Date: Wed, 15 Mar 2017 16:30:45 -0400
> 
> > Note that this cache was already broken for caching timestamps of
> > multiple machines behind a NAT sharing the same address.
> 
> That's the documented, well established, limitation of time-wait
> recycling.
> 
> People who enable it, need to consider this issue.
> 
> This limitation of the feature does not give us a reason to break the
> feature even further as a matter of convenience, or to remove it
> altogether for the same reason.
> 
> Please, instead, fix the bug that was introduced.

At least I can say I've seen many people enable it without understanding
its impact, confusing it with tcp_tw_reuse, and copy-pasting it from
random blogs and complaining about issues in production.

I agree that it's hard to arbiter between stupidity and flexibility
though :-/

Regards,
Willy