shed some responsibilities to the centralized controller.
OpenFlow is designed to be used
entirely within a single organization.
All the routers in an OpenFlow domain act as one entity. The controller
has godlike power over all the routers
it controls. You would not let someone
outside your sphere of trust have such
access. An ISP may use OpenFlow to
control its routers, but it would not
extend that control to the networks of
customers. An enterprise might use
OpenFlow to manage the network inside a large data center and have a different OpenFlow domain to manage
its WAN. ISPs may use OpenFlow to
run their patch of the Internet, but it
is not intended to take over the Internet. It is not a replacement for inter-ISP systems such as Border Gateway
The switch to OpenFlow is not expected to happen suddenly and, as
with all new technologies, may not be
adopted at all.
Centralizing route planning has
˲ Takes Advantage of Moore’s Law.
Not only are general-purpose computers cheaper and faster, but there
is more variety. In the Google presentation at the 2012 Open Networking Summit, Urs Höelzle said Google
does its route computations using the
Google compute infrastructure.
˲ Offers Deeper Integration.
End-to-end communication can occur
directly from the applications all the
way to the controller. Imagine if every
Web-based service in your enterprise
could forward bandwidth requirements to the controller, which could
then respond with whether or not the
request could be satisfied. This would
be a radical change over the “send and
pray” architectures in use today.
˲ Turns Network Hardware into a
Commodity. The CPU and RAM horsepower required by the device is a function of the speeds and number of ports
on the device as shipped. Therefore, it
can be calculated during design, eliminating the need to factor in slack.
Also, designing and manufacturing a
device with a fixed configuration (not
upgradable) is less expensive.
˲ Makes Algorithms Simpler. Rath-
er than making decisions based on in-
ference and relying on cooperating al-
gorithms, more-direct algorithms can
be used. A dictatorship is the most
efficient form of government. Sup-
pose the VoIP phones of the campus
EMS team should always get the band-
width they need. It is easier to direct
each router on campus to give EMS
phones priority than it is to develop
an algorithm whereby each router in-
fers which devices are EMS, verifies a
trust model, confirms that trust, and
allocates the bandwidth—and hopes
that the other routers are doing the
In the past smartphone vendors care-
fully controlled which applications
ran on their phones and had perfectly
valid reasons for doing so: quality of
apps, preventing instability in the
phone network, and protection of
their revenue streams. We can all see
now that the paradigm shift of permit-
ting the mass creation of apps did not
result in a “wild west” of chaos and
lost revenue. Instead, it inspired en-
tirely new categories of applications
and new revenue streams that exceed
the value of the ones they replaced.
Who would have imagined Angry
Birds or apps that monitor our sleep
patterns to calculate the optimal time
to wake us up? Apps are crazy, weird,
and disruptive—and I cannot imagine
a world without them.
Revisitng network I/O APIs: The netmap
SoC: Software, hardware, nightmare, Bliss
George Neville-Neil, Telle Whitney
TCP Offload to the Rescue
1. hoelzle, u. keynote speech at the open networking
summit (2012); http://www.youtube.com/
2. katti, s. openradio: virtualizing cellular wireless
infrastructure. presented at the open networking
summit (2012); http://opennetsummit.org/talks/
3. lin, g. Industry perspectives of sDn: technical
challenges and business use cases. presentation
at the 2012 open networking summit; http://
pdf (slides 6-7).
4. sIgComm Demo; http://www.openflow.org/
Thomas A. Limoncelli is an author, speaker, and
system administrator. his best-known books include
Time Management for System Administrators (o’reilly,
2005) and The Practice of System and Network
Administration, 2nd edition (addison-Wesley, 2007).
he works at google in new york City on the ganeti
project ( http://code.google.com/p/ganeti). see his blog