Subject: (IPng 6511) Re: Host Fragmentation

From: [email-masked]
Date: Wed, 23 Sep 1998 19:38:38 EDT

I have added the following 
<A HREF="http://members.aol.com/Telford001/#ANALYZE">analysis</A> to my
website. (I have also added
the first chapter of my <A HREF="http://members.aol.com/Telford001/#TEXTBOOK">
textbook</A> as well.  Some of the information may
be of interest, and I always appreciate comments.)

The C.R.I.T.I.C. Analyzes an IPv6 Design Choice

One of the most curious aspects of IPv6 is the prohibition on network
fragmentation even as the IPv6 permits host fragmentation, which the
receiver could not possibly distinguish from network
fragmentation. The point of such a prohibition is extremely hard to
understand. For massive web and file servers major performance wins
can be achieved with network fragmentation. We have seen the number of
clients served go from 10-12,000 clients per second to 16,000 clients
per second merely by configuring the server to use jumbograms on a
gigabit medium while an intermediate system performed network
fragmention.

Wayne Hathaway, Chief Architect of Alteon Networks, described the
issue quite well in a recent e-mail on the IPv6 mailing list.

    Nobody disputes that network devices should be able to fragment at
    full speed, nor do they dispute that given a large number of clients,
    each should be able to reassemble fast enough.
    
    So apart from the fragment loss question, the server could have been
    pumping its data into a giant bit bucket: the performance improvement
    came SOLELY from using jumbo frames on the server.
    
    And about fragment loss, nobody can expect to get top performance over
    a lossy net, and a decent TCP implementation could adapt to lossage
    with an end result that is guaranteed to be no worse than what IPv6
    limits you to, and may well be substantially better.
    
    Again I repeat: Is it reasonable for a protocol of the future to
    outlaw the use of network fragmentation simply because there are
    situations in which it might be bad with current router or host stack
    implementations?

During a recent discussion on the IPv6 mailing list, several opponents
of permitting network fragmentation justified their position by
reference to <A HREF="http://members.aol.com/Volsinians/fragcomments.pdf">
Fragmentation Considered Harmful</A>, which I have made
available with some comments to relate the 1987 analysis in the
document with the realities of today's 1998 Internet.

The document is practically useless as an input into the design of the
protocol of the future. None of the analysis actually indicates any
real flaws with fragmentation as a procedure when it is used
properly. Almost all the problems identified in this paper are
problems associated with 1987 software and hardware including without
limitation:

    * buggy 1987 implementations of the Berkeley network layer, 

    * some questionably implemented pronet-10 or pronet-80 adapter
      cards of the 1985-7 time frame and 

    * memory starved routers of the same time frame.

The paper should never have been used as an input to the design of IPv6.

Joachim Martillo
<A HREF="http://members.aol.com/Telford001/">Telford Tools, Inc.</A> 
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