Re: Problem of blocking ICMP packets

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On Tue, 11 May 2004 03:48:57 +0900
Masataka Ohta <mohta@xxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:

> Mark Smith;
> 
> >>>A number of commercial
> >>>products and applications do rely on PMTU to work, and will
> >>>do an PATH MTU discovery, and send the MTU sized packets
> >with>>DF (don't frag).
> >>
> >>and send packets larger than MTU expecting to receive ICMP
> >>errors in vain.
> >>
> >>Read the original mail of the thread on the reality.
> 
> > The problem identified has nothing to do with the concept or
> > typical implementations of PMTUD being broken.
> 
> Wrong.

Ok, if you think I'm wrong, what is it that is preventing PMTUD
working, as per the RFC method of operation, in this discussion ?


> 
> > RFC1192 (http://www.rfc-editor.org/rfc/rfc1191.txt) is the
> > spec for PMTUD. 
> 
> Read the RFC.

> 
> It says "To detect increases in a path's PMTU, a host
> periodically increases its assumed PMTU".

And how does the host know that it has increased the PMTU too far
? 

I'm really interested in some references to documentation or
information that has helped you form your opinion. I'm keen to
find out if my understanding of PMTUD purpose and operation is
incorrect.

Here is a summary of the references I've cited, including an
additonal one, for further information :

(a) The RFC of course. This is the reference for PMTUD operation.

(b) Radia Perlman's book, "Interconnections", 2nd Edition. Pg
185, section 8.7. There is also some discussion of fragmentation
- related to PMTUD - on page 233, section 10.4.7

and an additional one

(c) W. Richard Stevens' book, "TCP/IP Illustrated, Volume 1".
Page 340, Section 24.2


Regards,
Mark.

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