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Date: Mon, 02 May 2005 16:48:35 +0200
From: Andre Oppermann <andre@freebsd.org>
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To: Qing Li <qingli@speakeasy.net>
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cc: 'David Malone' <dwmalone@maths.tcd.ie>
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Subject: Re: FW: pmtu patch
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Qing Li wrote:
> -----Original Message-----
> From: Qing Li [mailto:qingli@FreeBSD.org]
> Sent: Thursday, April 28, 2005 5:36 PM
> To: andre@freebsd.org
> Cc: qingli@freebsd.org
> Subject: pmtu patch
> 
>     Hi Andre,
> 
>     I was thinking whether we could add another variable
>     in "hc_metrics" called "u_long rmx_mtu_lastupdate" and
>     perhaps a new function called "tcp_hc_getmtu_update"
> 
>     When we get the ICMP PRC_MSGSIZE notification, we do
> 
>     if (((time_second() - tcp_hc_getmtu_update(&inc)) < PMTU_MIN)
>         do_nothing;
>     else {
>       ...
>     }
> 
>     If there is no suggested mtu value, instead of immediately
>     falling back to the default, or rely on the original
>     packet fragment, can we just use the mtu value in the
>     host cache as the basis for the next try as in:
> 
>     else {
> 
>         <set new value for rmx_mtu_lastupdate>
> 
>         mtu = ip_next_mtu(tcp_hc_getmtu(&inc), 1);
> 
>     }

IMO this is too complicated for too little actual value.  It's not
that we are supposed to run into this problem all the time.  David's
idea provides a very easy way to work around the problem without
requiring any state tracking.

-- 
Andre