netdev - Re: [RFC PATCH] network: return errors if we know tcp

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Date:	Mon, 15 Nov 2010 11:32:10 +0100
From:	Patrick McHardy <kaber@...sh.net>
To:	Hua Zhong <hzhong@...il.com>
CC:	'Eric Paris' <eparis@...hat.com>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, davem@...emloft.net,
	kuznet@....inr.ac.ru, pekkas@...core.fi, jmorris@...ei.org,
	yoshfuji@...ux-ipv6.org
Subject: Re: [RFC PATCH] network: return errors if we know tcp_connect failed

On 13.11.2010 00:14, Hua Zhong wrote:
>> On 11.11.2010 22:58, Hua Zhong wrote:
>>>> Yes, I realize this is little different than if the
>>>> SYN was dropped in the first network device, but it is different
>>>> because we know what happened!  We know that connect() call failed
>>>> and that there isn't anything coming back.
>>>
>>> I would argue that -j DROP should behave exactly as the packet is
>> dropped in the network, while -j REJECT should signal the failure to
>> the application as soon as possible (which it doesn't seem to do).
>>
>> It sends an ICMP error or TCP reset. Interpretation is up to TCP.
> 
> Huh? It's the OUTPUT chain we are talking about. There is no ICMP error or
> TCP reset.

Of course there is.

ICMP (default):

iptables -A OUTPUT -p tcp -j REJECT

TCP reset:

iptables -A OUTPUT -p tcp -j REJECT --reject-with tcp-reset

The second one will cause a hard error for the connection.
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