netdev - Re: [PATCH 2.6.22] TCP: Make TCP_RTO

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Date:	Thu, 12 Jul 2007 14:27:05 -0700
From:	Rick Jones <rick.jones2@...com>
To:	Stephen Hemminger <shemminger@...ux-foundation.org>
Cc:	noboru.obata.ar@...achi.com, David Miller <davem@...emloft.net>,
	yoshfuji@...ux-ipv6.org, netdev@...r.kernel.org
Subject: Re: [PATCH 2.6.22] TCP: Make TCP_RTO_MAX a variable (take 2)

> One question is why the RTO gets so large that it limits failover?
> 
> If Linux TCP is working correctly,  RTO should be srtt + 2*rttvar
> 
> So either there is a huge srtt or variance, or something is going
> wrong with RTT estimation.  Given some reasonable maximums of
> Srtt = 500ms and rttvar = 250ms, that would cause RTO to be 1second.

I suspect that what is happening here is that a link goes down in a 
trunk somewhere for some number of seconds, resulting in a given TCP 
segment being retransmitted several times, with the doubling of the RTO 
each time.

rick jones
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