On Jan 15, 2014, at 9:37 AM, "Dobbins, Roland" <rdobb...@arbor.net> wrote:
> But what I'm saying is that that whether or not they want to use jumbo frames
> for Internet traffic, it doesn't matter, because PMTU-D is likely to be
> broken either at the place where the traffic is initiated, the place where
> the traffic is received, or both - so any nonsense in the middle, especially
> on IXP networks in particular, isn't really a significant issue in and of
> itself.
Your assertion does not match my deployment experience.
When I have deployed endpoints that have working PMTU-D, I have 99.999% success
with the ISP's in the middle having working PMTU-D. It even works fine for 9K
providers connected to 1500B exchange points, because the packet-too-big
typically originates from the input side of the router (the backbone link to
the IXP router). Indeed, the only place I've seen it broken is where the ISP
9K peers at an exchange, and the "far end" ISP runs a < 9K backbone (like
4470), so the far end IXP-router does the packet-to-big, and originates it from
the exchange LAN, which because it's no longer in the table fails to past uRPF.
(Business class) ISP's don't break PMTU-D, end users break it with the
equipment they connect. So a smart user connecting equipment that is properly
configured should be able to expect it to work properly.
--
Leo Bicknell - bickn...@ufp.org - CCIE 3440
PGP keys at http://www.ufp.org/~bicknell/
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