netdev - Re: BSD 4.2 style TCP keepalives

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Message-Id: <20100106.165933.226786062.davem@davemloft.net>
Date:	Wed, 06 Jan 2010 16:59:33 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	ilpo.jarvinen@...sinki.fi
Cc:	netdev@...r.kernel.org, nhorman@...driver.com
Subject: Re: BSD 4.2 style TCP keepalives

From: "Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
Date: Thu, 7 Jan 2010 02:34:51 +0200 (EET)

> On Wed, 6 Jan 2010, David Miller wrote:
> 
>> 3) tcp_data_queue() should make it to, and hit, this conditional:
>> 
>> 	if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
>> 
>>    which will schedule an ACK the same exact way we would if
>>    tcp_sequence() rejected the sequence range.
>> 
>> So it's a mystery why we aren't responding to Windows 2000's
>> BSD 4.2 style zero window probes.
>> 
>> Can someone please validate my analysis?
> 
> In 3) I don't see why we'd hit that one as peer's snd_una+1 would be 
> larger than rcv_nxt.

Peer constructs keepalive packet using sequence [snd.una-1,snd.una],
both of which are <= rcv_nxt
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