Subject: [IMRG] RE: Internet measurement: what next? - Designing for Visibility

From: "Loki Jorgenson" <[email-masked]>
Date: Thu, 3 Jul 2003 12:38:27 -0700

Mark - a theme worth considering IHMO is designing networks for
visibilty.

Many of the best and most basic sources of network intelligence are
being impacted by changes in network design.  Take ICMP for example - it
is effectively the nervous system of the networks.  It does the job of
feedback for network components.  In some ways, it is like tactile
sensation in the human body that allows us to interact effectively (and
safely) with our environment.

However, even the simplest means, such as ping and traceroute, are being
affected by the use of VPNs and VLANs, traffic shaping and filtering,
aggregate routing with multiple peering points, ICMP blocking, parallel
channels on routers, lightpaths, etc.  Obviously there are reasons and
benefits for these technologies to be introduced.  Security is one of
the driving forces.  At one extreme, ICMP may be blocked completely -
this is a bit like numbing all the nerves in the body in order to avoid
pain.  There is a balance to be struck.

Currently the means to effective monitoring, measurement,
troubleshooting and tuning are actively being developed.  Most rely on
the essential (and changing) nature of networks at various layers.  Some
require access to networks that aren't always feasible or have limiting
constraints (e.g. you must own the hardware).  Networks can support
these capabilities better or worse in the future.

And then there are all kinds of proposals/drafts that would affect
stacks, hardware, and application design and might provide new forms of
feedback.  These typically require widespread adoption and even then the
overall macroscopic consequences are not well understood (e.g. what does
a world of coexisting legacy and Fast TCP stacks look like?).  What do
they offer?

So, going forward, one of the chief questions then becomes "How can
(typical/IP) networks be optimized for various benefits including
effective feedback mechanisms that support monitoring, measurement,
diagnosis and tuning?"   In a future with self-healing or self-tuning
networks, this seems tremendously important.

I would be interested to hear if any comments....

Loki Jorgenson
Director, Research
jaalaM Technologies
t   604 433 2333 ext 105
m   604 340-2480

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From: Jennifer Rexford <[email-masked]>
Date: Sun, 6 Jul 2003 23:48:44 -0400 (EDT)

> a theme worth considering IHMO is designing networks for visibilty.

I think that's a great point.  Measurement has been largely an
afterthought (and an "add on") in designing IP networks and, as such,
our visibility is pretty limited and imperfect.  In some cases, we can
"add" measurement by tapping the network or monitoring the protocols.
But, troubleshooting problems in the network is much harder and it
would be interesting to think of how to extend the equipment and the
protocols to report more information (e.g., error messages, protocol
annotations, etc.) that would help in diagnosing problems -- or to
better enable active tools like traceroute to work.

> channels on routers, lightpaths, etc.

Good point.  Along these lines, a group of us have been working on 
a tool that reports the sequence of Autonomous Systems (ASes) on a
forwarding path, to help in determining which AS (or ASes) or
involved.  See

  Z. M. Mao, J. Rexford, J. Wang, and R. H. Katz, "Towards an
  Accurate AS-Level Traceroute Tool," to appear in Proc. ACM
  SIGCOMM, August 2003.
    http://www.research.att.com/~jrex/papers/sigcomm03.ps
    http://www.research.att.com/~jrex/papers/sigcomm03.pdf

In the context of your posting, the main point is really how hard the
problem is to solve, even partially.  If only ICMP reply messages were
sent consistently and included the AS number of the sending router... ;)

-- Jen