IP Fragmentation - Not reliable over the Internet?

Owen DeLong owen at delong.com
Tue Aug 27 18:47:15 UTC 2013


On Aug 27, 2013, at 07:33 , Valdis.Kletnieks at vt.edu wrote:

> On Tue, 27 Aug 2013 00:34:57 -0700, Owen DeLong said:
>> That's a lot of questions he didn't ask.
> 
> This isn't your first rodeo.  You should know by now that the question
> actually asked, the question *meant* to be asked, and the question that
> actually needed answering are often 3 different things.
> 
>> If I send a packet out as a legitimate series of fragments, what is the chance
>> that they will get dropped somewhere in the middle of the path between the
>> emitting host and the receiving host?
> 
>> To my thinking, the answer to that question is basically "pretty close to 0 and
>> if that changes in the core, very bad things will happen."
> 
> Saku Ytti and Emile Aben have numbers that say otherwise.  And there must
> be a significantly bigger percentage of failures than "pretty close to 0",
> or Path MTU Discovery wouldn't have a reputation of being next to useless.

No, their numbers describe what happens to single packets of differing sizes.

Nothing they did describes results of actually fragmented packets.

Owen




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