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Re: PMTU info

To: netdev@xxxxxxxxxxx
Subject: Re: PMTU info
From: Michael Richardson <mcr@xxxxxxxxxxxxxxxxxxxxxx>
Date: Sun, 10 Feb 2002 11:00:59 -0500
In-reply-to: Your message of "Sun, 10 Feb 2002 07:59:28 +0100." <20020210075928.A22000@wotan.suse.de>
Sender: owner-netdev@xxxxxxxxxxx
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>>>>> "Andi" == Andi Kleen <ak@xxxxxxx> writes:
    Andi> On Fri, Feb 08, 2002 at 03:59:37PM -0500, Michael Richardson wrote:
    >> -----BEGIN PGP SIGNED MESSAGE-----
    >> 
    >> 
    >> >>>>> "Andi" == Andi Kleen <ak@xxxxxxx> writes:
    Andi> On Thu, Feb 07, 2002 at 05:59:45PM -0500, Michael Richardson wrote:
    >> >> We think that /proc/net/rt_cache might have info, but we don't >>
    >> see it. Is there another place that we should look?
    >> 
    Andi> /proc/net/rt_cache has a MTU column. You can also get it via ip
    Andi> route get <ip address>
    >>
    Andi> route --cache unfortunately doesn't show it.
    >> Do they expire very quickly? Can we extend it? Is there some debugging
    >> we can enable to log the MTU changes? Does it get deleted when the TCP
    >> connection gets closed?

    Andi> Depends on your workload.  Normally not.

  Is the timeout configurable somewhere?
  What kind of work would affect our workload.

    Andi> Just add a few printks.
 
  I was considering heading in that direction. Would some printk's and a
patch to enable them via some sysctl be welcome?

  Adding printk's helps for debugging this, but it does not help us do
regression tests of non-hacked kernels :-)

  We use User-Mode-Linux builds such that we can easily capture console
output and control ethernet I/O. Having to apply additional patches to the
kernel kind of defeats this.

]       ON HUMILITY: to err is human. To moo, bovine.           |  firewalls  [
]   Michael Richardson, Sandelman Software Works, Ottawa, ON    |net architect[
] mcr@xxxxxxxxxxxxxxxxxxxxxx http://www.sandelman.ottawa.on.ca/ |device driver[
] panic("Just another NetBSD/notebook using, kernel hacking, security guy");  [


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