netdev - Re: Change in IPv4 TCP reset behavior after kernel upgrade

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Date:	Wed, 4 Dec 2013 10:15:00 -0500
From:	Neal Cardwell <ncardwell@...gle.com>
To:	Fiedler Roman <Roman.Fiedler@....ac.at>
Cc:	"davem@...emloft.net" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: Change in IPv4 TCP reset behavior after kernel upgrade

On Wed, Dec 4, 2013 at 5:09 AM, Fiedler Roman <Roman.Fiedler@....ac.at> wrote:
> Hello,
>
> After upgrading from linux-image-3.10.17 to linux-image-3.10.21 I noticed, that afterwards reset packets started to be transmitted with ID != 0. For testing:
>
> tcpdump -i eth0 -nn -s0 -X -vvv 'tcp[tcpflags] & tcp-rst != 0'
>
> I did a short search to find out when and why this was changed (PATCH), but did not get any wiser.
>
> Was this an intended change, e.g. to increase resilience against RST-packet injection/DOS scenarios? Is it just accidentally?
>
> The ID seems to be in sequence, so it is not uninitialized memory content.
>
> Roman
>
> PS: The kernel was patched with the vserver-patch, this might have an influence. I did not have time yet to build a kernel without that modification.

One possibly related commit would be:

ip: generate unique IP identificator if local fragmentation is allowed
703133de331a7a7df47f31fb9de51dc6f68a9de8

http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=703133de331a7a7df47f31fb9de51dc6f68a9de8

But that went into 3.10.16, which is one release outside the window
you mention....

neal
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