Re: [v6ops] PMTUD issue discussion

"Templin, Fred L" <Fred.L.Templin@boeing.com> Tue, 26 August 2014 15:43 UTC

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From: "Templin, Fred L" <Fred.L.Templin@boeing.com>
To: Fernando Gont <fgont@si6networks.com>, "Fred Baker (fred)" <fred@cisco.com>, Andrew 👽 Yourtchenko <ayourtch@gmail.com>
Thread-Topic: [v6ops] PMTUD issue discussion
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Date: Tue, 26 Aug 2014 15:42:51 +0000
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References: <0D370E74-688B-4EB3-A691-309A03AF20BA@cisco.com> <53FBA174.2040302@isi.edu> <53FBA6E1.90905@bogus.com> <CAPi140PMeM9omtm11+NHa2ywUfof_tE7HknKExtoEb32mm7L_w@mail.gmail.com> <71D0D5E8-80E9-430B-8ED4-16C1F99082CC@cisco.com> <53FCA926.9080206@si6networks.com>
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Subject: Re: [v6ops] PMTUD issue discussion
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Hi Fernando,

> -----Original Message-----
> From: v6ops [mailto:v6ops-bounces@ietf.org] On Behalf Of Fernando Gont
> Sent: Tuesday, August 26, 2014 8:35 AM
> To: Fred Baker (fred); Andrew 👽 Yourtchenko
> Cc: IPv6 Ops WG
> Subject: Re: [v6ops] PMTUD issue discussion
> 
> Hi, Fred,
> 
> On 08/26/2014 12:13 PM, Fred Baker (fred) wrote:
> >> I think it would be useful to see the discussion of this measure
> >> and its applicability/tradeoffs in the draft.
> >
> > It seems like it might have value to also test the interaction
> > with various initial window settings, and look at its inclusion in
> > other relevant OS’s including FreeBSD, Windows, and MacOSX.
> 
> FWIW, while RFC4821 can work without relying on PLPMTUD at all, some
> OSes (such as Windows) only fall back to ICMP-less PMTUD as part of
> "ICMP blackhole detecion" -- and they have been doing this for years
> now...

I think the point is that PLPMTUD is not well supported in modern
OSes in the spirit in which it was specified in RFC4821. That
needs to change.

Thanks - Fred
fred.l.templin@boeing.com

> > My reading of 4821 says it’s grand theory, but I’m not precisely
> > sure how I would write the code. As an initial setting, for
> > example, I could imagine sending an initial burst containing a 9K
> > byte packet, a 1500 byte
> 
> Unlikely if the underlying link-layer technology is Ethernet (PMTUD
> will never be assumed to be larger than your own MTU).
> 
> Additionally, I doubt you'd employ different packet
> sizes/assumed_PMTUDs all at once.
> 
> Thanks,
> --
> Fernando Gont
> SI6 Networks
> e-mail: fgont@si6networks.com
> PGP Fingerprint: 6666 31C6 D484 63B2 8FB1 E3C4 AE25 0D55 1D4E 7492
> 
> 
> 
> 
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