Subject: (IPng 6419) Host Fragmentation

From: [email-masked]
Date: Thu, 10 Sep 1998 05:37:51 EDT

The article attached below that I recently received suggests that
the IPv6 rule of only fragmenting at the source host really is
rather ill-conceived.

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

Subject: Microsoft NT and Alteon blurb

http://www.infoworld.com/cgi-bin/displayStory.pl?980817.ehntlargeframe.htm

  Microsoft claims large frames help boost NT's performance

  By Stephen Lawson
  InfoWorld Electric

  Posted at 6:47 AM PT, Aug 17, 1998
  Tests by Microsoft last week are claimed to show that Windows NT 4.0
  server's performance can be boosted to nearly a full 1Gbps by
  large-frame Ethernet technology, breaking through current performance
  limits.

  Microsoft officials said they achieved 920Mbps throughput on a server
  using the AceNIC 180, a Gigabit Ethernet network interface card from
  Alteon, which also supplied the proprietary jumbo-frame technology.

  Large Ethernet frames can improve the efficiency of Gigabit Ethernet
  by reducing the number of frames that must be created and forwarded.
  Packing more data in a single frame can boost performance on
  server-to-server applications, transmitting large amounts of data in
  one stream, such as backups and replication.

  One user expressed surprise at the throughput achieved in Microsoft's
  tests.

  "If that's the case, it's quite a feat," said Lee Damon, a senior
  systems administrator at Qualcomm, in San Diego.

  The tests were conducted using a single-processor Intel 400-MHz
  Xeon-based server and four 333-MHz Pentium II clients. An Alteon
  Gigabit Ethernet server switch connected the servers and clients.

  Earlier tests using standard Ethernet frames have shown performance
  from 500Mbps to 600Mbps, said Reza Baghai, NT performance lead
  engineer at Microsoft.

  Alteon is the only Gigabit Ethernet vendor currently supporting large
  Ethernet frames. However, Baghai said Microsoft has had discussions
  with other vendors about using large frame sizes.

  According to Baghai, the standard NDIS driver set for NT 4.0, as well
  as Windows 98, can support large frames without modification.

  Baghai also confirmed that some developments due in NT 5.0 are
  designed to boost server throughput.

  A checksum off-load feature that can move TCP checksum processing from
  the CPU to the adapter will reduce the load on the server CPU. Another
  feature will deserialize the sending path, which allows a
  dual-processor server to send data from both processors at the same
  time.

  Analysts said large frame sizes could be beneficial to large
  enterprises with centralized server farms and for organizations that
  require high-bandwidth Web serving.

  Microsoft Corp., in Redmond, Wash., can be reached at
  http://www.microsoft.com. Alteon Networks Inc., in San Jose, Calif.,
  can be reached at http://www.alteon.com.

  Stephen Lawson is a senior writer for InfoWorld.

                     Go to the Week's Top News Stories

 Please direct your comments to InfoWorld Deputy News Editor, Carolyn April

                Copyright ) 1998 InfoWorld Media Group Inc.

                  InfoWorld Electric is a member of IDG.net

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---

From: "Matt Crawford" <[email-masked]>
Date: Thu, 10 Sep 1998 08:50:38 -0500

> [Article about high-MTU media helping an OS with an immature IP
> stack deleted.]

I see no implications there for fragmentation at the source instead
of at a router.  In fact, nothing in the article states that IP was
used for the comparison at all.
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---

From: James Carlson <[email-masked]>
Date: 10 Sep 1998 10:01:08 -0400

> the IPv6 rule of only fragmenting at the source host really is

Huh?

The load on the receiver is the same for a given medium's MTU,
regardless of whether the host did the fragmentation or an
intermediate router did it.  This leaves only the effort involved in
fragmenting on transmission as the distinguishing factor for IPv6's
lack of fragmentation.  Saying that network performance is more
affected by the speed at which things can be sent than it is by the
burden of receiving the data is a rather suspect claim.  In fact, it's
almost certainly false.

The only things that this article might suggest to me would be:

	- Larger MTUs are better than smaller ones if throughput is
	  your goal (certainly not a surprise)

	- NT doesn't keep up with standard Gb Ethernet (probably not a
	  surprise)

-- 
James Carlson, Consulting S/W Engineer  <[email-masked]>
IronBridge Networks / 55 Hayden Avenue  71.246W    Vox:  +1 781 372 8132
Lexington MA  02421-7996 / USA          42.423N    Fax:  +1 781 372 8190
"PPP Design and Debugging" --- http://people.ne.mediaone.net/carlson/ppp

---

From: Thomas Narten <[email-masked]>
Date: Thu, 10 Sep 1998 13:56:25 -0400

> the IPv6 rule of only fragmenting at the source host really is

Before getting all excited by this "new" revelation, it might not hurt
to go review an ancient article called "fragmentation considered
harmful" by Kent & Mogul published way back in SIGCOMM 87.

Thomas