[e2e] MTU - IP layer

Loki Jorgenson ljorgenson at apparentnetworks.com
Thu Apr 21 23:57:53 PDT 2005

OK - I've skimmed the latest draft of the RFC and I see better how they
are planning to make this work.  It represents a much more significant
change than I had gleaned from earlier readings. 

I'm still wondering about how the loss of these (disposable) probes will
be distinguished from congestion and other forms of loss, how the local
host's record of PMTU will change if the actual PMTU changes (for
example route change), and various other scenarios involving interplay
between loss, TCP and PLPMTUD .... but I'll just finish reading the
current draft and find out how it all turns out.

If others are as curious:

In any case, thanks for your insights Joe.

-----Original Message-----
From: Joe Touch [mailto:touch at ISI.EDU] 
Sent: Thursday, April 21, 2005 9:48 PM

The new ptmud is based on the presence of "yes, it got through"
feedback. The loss isn't what matters; it's what gets through that does
(successful probes). The algorithm says "stay small, and try large
(disposable) probes; if the probes work, THEN get larger". This is not
susceptible to black holes - it works only when both the probes get
through _and_ the feedback makes it back successfully.


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