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<div class="moz-cite-prefix">Lorenzo Colitti wrote on 18/01/2013
06:18:<br>
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cite="mid:CAKD1Yr38GaMmryEmvHW-6pZN10TH+VJar2ru1Ch-LpcUFtezxw@mail.gmail.com"
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<div class="gmail_default" style="">On Fri, Jan 18, 2013 at 2:08
AM, Sam Wilson <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:Sam.Wilson@ed.ac.uk" target="_blank">Sam.Wilson@ed.ac.uk</a>></span>
wrote:<br>
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<div class="h5"><span style="color:rgb(34,34,34)">In
principle PMTUD is the more technically elegant way
- finding out what's out there and adapting to it.
Mandating a fixed MTU is actually not simple since
I guess you'd have to allow for tunnelling,
extension headers and so on that might be added
along the path and which would rob space from the
data field. You'd have to require a physical MTU
larger than the logical MTU with enough headroom to
allow for extra overhead, and *still* have a method
of dealing with any overflows en route caused by,
say, multiple layers of tunnelling.</span><br>
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It all gets a bit awkward.</blockquote>
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<div style="">Agreed. Reality is often messy.</div>
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<div style="">My personal opinion is that we should rely on
path MTU to work but, due to the latency impact, try not
to rely on it too often (and so, for example, lower the RA
MTU on networks that *know* they are behind a tunnel).</div>
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<div style="">I don't know how many people agree with me
though. And I also don't know if we can depend on PMTUD to
work if we don't rely on it often.</div>
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Imho, this (use of RA MTU) is the easiest way to go in every case.
This should either be hardcoded or computed from the WAN link.<br>
As an extra step, someone could have a larger MTU to be advertised
for local attached networks.<br>
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--<br>
Tassos<br>
<br>
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