netdev - Re: [RFC PATCH net-next] tcp: introduce tcp_tw_interval to specifiy the time of TIME-WAIT

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Date:	Tue, 09 Oct 2012 11:42:16 +0800
From:	Cong Wang <amwang@...hat.com>
To:	Neil Horman <nhorman@...driver.com>
Cc:	netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	Patrick McHardy <kaber@...sh.net>,
	Eric Dumazet <edumazet@...gle.com>
Subject: Re: [RFC PATCH net-next] tcp: introduce tcp_tw_interval to specifiy
 the time of TIME-WAIT

On Mon, 2012-10-08 at 10:07 -0400, Neil Horman wrote:
> On Mon, Oct 08, 2012 at 11:17:37AM +0800, Cong Wang wrote:
> > On Tue, 2012-10-02 at 08:09 -0400, Neil Horman wrote:
> > > No, its not very friendly, but the people using this are violating the RFC,
> > > which isn't very friendly. :)
> > 
> > Could you be more specific? In RFC 793, AFAIK, it is allowed to be
> > changed:
> > 
> > http://tools.ietf.org/html/rfc793
> > 
> > " To be sure that a TCP does not create a segment that carries a
> >   sequence number which may be duplicated by an old segment remaining in
> >   the network, the TCP must keep quiet for a maximum segment lifetime
> >   (MSL) before assigning any sequence numbers upon starting up or
> >   recovering from a crash in which memory of sequence numbers in use was
> >   lost.  For this specification the MSL is taken to be 2 minutes.  This
> >   is an engineering choice, and may be changed if experience indicates
> >   it is desirable to do so."
> > 
> Its the length of time that represents an MSL that was the choice, not the fact
> that reusing a TCP before the expiration of the MSL is a bad idea.
> 
> > or I must still be missing something here... :)
> > 
> Next paragraph down:
> 	This specification provides that hosts which "crash" without
>     retaining any knowledge of the last sequence numbers transmitted on
>     each active (i.e., not closed) connection shall delay emitting any
>     TCP segments for at least the agreed Maximum Segment Lifetime (MSL)
>     in the internet system of which the host is a part.  In the
>     paragraphs below, an explanation for this specification is given.
>     TCP implementors may violate the "quiet time" restriction, but only
>     at the risk of causing some old data to be accepted as new or new
>     data rejected as old duplicated by some receivers in the internet
>     system. .... etc.
> 
> 

Ah, ok. Thanks for the detailed answer!


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