netdev - Re: tcp_reordering as 0 possible?

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Message-ID: <alpine.DEB.2.00.1003171333250.19416@melkinpaasi.cs.helsinki.fi>
Date:	Wed, 17 Mar 2010 13:38:15 +0200 (EET)
From:	"Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
To:	raj ravi <mekaviraj@...il.com>
cc:	netdev@...r.kernel.org
Subject: Re: tcp_reordering as 0 possible?

On Mon, 15 Mar 2010, raj ravi wrote:

> what is the behaviour in TCP stack if I set tcp_reordering as 0.
> So , sender will  start retransmission without waiting for any duplicate ACK ?
> /proc/sys/net/ipv4/tcp_reordering   - Please clarify.
> The default value is 3 which means it waits until 3 duplicate ack's
> arrive and then start retransmission.
> 
> "The TCP sender should use the fast retransmit algorithm to detect and
> repair loss based on incoming duplicate ACKs. After the arrival of 3
> duplicate ACKs (4 identical ACKs without the arrival of any other
> intervening packet), TCP performs a retransmission of what appears to
> be the missing segment, without waiting for the retransmission timer
> to expire."

Depends on other things quite much but for a typical transfer you'd still 
need one duplicate ACK to trigger actual recovery. However, in general 
root is not (always) forbidden to set non-sensical values for sysctls.

-- 
 i.
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