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Date: Thu, 07 Dec 2000 11:00:50 -0800
From: Julian Elischer <julian@elischer.org>
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To: Patrick Bihan-Faou <patrick@netzuno.com>
Cc: freebsd-net@freebsd.org
Subject: Re: Problem with PPP, tcpmssd and routing socket messages
References: <POEDLEGGIEKJJIOGHEJNAEINCDAA.patrick@netzuno.com>
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Patrick Bihan-Faou wrote:
> 
> Hi,
> 
> I am playing around with tcpmssd and an ADSL link.
> I use tcpmssd with the "-i" option to indicate which interface it should
> obtain the MTU information from. With this option, tcpmssd starts listening
> to the routing socket and updates its knowledge of the MTU based on the
> information received from the routing socket.

ppp now has tcpmssd build in (in at least one version... 
check with brian@freebsd.org)
> 
> The problem is that tcpmssd is started before the ppp negotiation is
> finished, so the initial MTU information is "incorrect" (1500). When the PPP
> negotiation is done, the MTU for the tun0 interface is updated to the
> correct value (1492) (as shown in ifconfig), but tcpmssd never receives any
> notification of that fact.
> 
> The only routing update related to the tun0 interface that is received by
> tcpmssd is the "NEWADDR" message indicating the negotiated IP address, I do
> not see any IFINFO messages (which are the ones used for the MTU updates).
> 
> If I update the MTU manually (using ifconfig), everything works fine:
> tcpmssd receives the RTM_IFINFO messages and the new MTU is used.
> 
> Am I missing something ? Is the routing socket supposed to be "reliable" or
> can some messages get lost ? Does the fact that multiple processes are
> listening on the routing socket (natd etc.) changes the behaviour ?
> 
> I am a bit lost here, I looked at the ppp code and the kernel code that does
> the MTU updates and the way I understand it, there should always be a
> routing message generated, however I can not see it anywhere...
> 
> Patrick.
> 
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-- 
      __--_|\  Julian Elischer
     /       \ julian@elischer.org
    (   OZ    ) World tour 2000
---> X_.---._/  presently in:  Budapest
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