linux-kernel - Re: [PATCH v3] net: Use standardized (IANA) local port range

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Message-ID: <20200829103715.iofmvtisabjl5hqb@lion.mk-sys.cz>
Date:   Sat, 29 Aug 2020 12:37:15 +0200
From:   Michal Kubecek <mkubecek@...e.cz>
To:     Bart Groeneveld <avi@...tavi.nl>
Cc:     linux-kernel@...r.kernel.org,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        netdev@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH v3] net: Use standardized (IANA) local port range

On Fri, Aug 28, 2020 at 10:44:47PM +0200, Bart Groeneveld wrote:
> This change will effectively halve the available ephemeral ports,
> increasing the risk of port exhaustion. But:
> ...
> b) It is only an issue with more than 11848 *outgoing* connections.
> 	I think that is a niche case (I know, citation needed, but still).

You don't need 11848 simultaneous connections to run into problems as
you may also have timewait sockets left after a connection is closed.
If there are many shortlived outgoing connections to the same server,
you may run out of ephemeral ports even without having too many active
connections at any time.

Michal