Probe interval Was: [pmtud] draft PMTUD minutes from IETF64

On Fri, Dec 09, 2005 at 01:51:52AM -0500, Matthew J Zekauskas wrote:
> Matt Mathis started a discussion around one of the open technical issues
> in the draft: how often should you probe to see if the MTU has been raised
> along a path.   The draft currently says five minutes, but that value
> was somewhat arbitrary.  Matt wondered if anyone has insights into
> existing precedent or a rational way of picking a number.
> Michael Richardson thought 5 minutes sounded about right, and in
> any case it should be greater than the 2 minute TCP timeout; he
> also thought it should not be larger than the typical damping interval
> for BGP.  John Heffner commented that ten minutes is commonly used for
> values in route caches.  Fernando Gont suggested a strategy being considered
> for OpenBSD: base the probe interval based on the current MTU size.  If the
> size is small, probe more frequently; if the value is large (and still
> working) use a larger timeout.  Matt asked if Fernando considered 1500
> large or small.  Fernando thought "small", and a "large" value might
> be something greater than 6000 right now; a value of 10 to 15 minutes
> might be appropriate there.  Dave Thalor noted that since the draft
> is an extension of "PMTUD classic" right now, RFC 1981 says 10 minutes,
> so that's a value that you would not have to defend.

What about specifying a bitrate by considering all probes lost. So
PMTUd-new shouldnt sent out more than 100 bit/s additional traffic.
Which makes it 2 Minutes for 1500 byte probes. (1500 * 8 / 120)

Flo
-- 
Florian Lohoff                  flo@rfc822.org             +49-171-2280134
                        Heisenberg may have been here.

Probe interval Was: [pmtud] draft PMTUD minutes from IETF64

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