Publications Technical Report

New tech report “Detecting Internet Outages with Active Probing”

We just published a new technical report “Detecting Internet Outages with Active Probing”, available at

From the abstract:

With businesses, governments, and individuals increasingly
dependent on the Internet, understanding its reliability is more
important than ever. Network outages vary in scope and
cause, from the intentional shutdown of the Egyptian Inter-
net in February 2011, to outages caused by the effects of
March 2011 earthquakes on undersea cables entering Japan,
to the thousands of small, daily outages caused by localized
accidents or human error. In this paper we present a new
method to detect network outages by probing entire blocks.
Using 24 datasets, each a 2-week study of 22,000 /24 address
blocks randomly sampled from the Internet, we develop new
algorithms to identify and visualize outages and to cluster
those outages into network-level events. We validate our ap-
proach by comparing our data-plane results against control-
plane observations from BGP routing and news reports, ex-
amining both major and randomly selected events. We con-
firm our results are stable from two different locations and
over more than one and half years of observations. We show
that our approach of probing all addresses in a /24 block is
significantly more accurate than prior approaches that use a
single representative for all routed blocks, cutting the num-
ber of mistake outage observations from 44% to under 1%.
We use our approach to study several large outages such as
those mentioned above. We also develop a general estimate
for how much of the Internet is regularly down, finding about
0.3% of the Internet is likely to be unreachable at any time.
By providing a baseline estimate of Internet outages, our
work lays the groundwork to evaluate ISP reliability.

Citation: Lin Quan and John Heidemann. Detecting Internet Outages with Active Probing. Technical Report N. ISI-TR-672. USC/Information Sciences Institute, May 2011. http://


New Video About Address Utilization and Allocations on Map Browser

The ANT project released a video describing Internet address allocation and how we study address utilization with IPv4 censuses. Aniruddh Rao prepared this video, working with John Heidemann and Xue Cai.

a scene from the ANT video describing address allocation and census taking

We have also updated our web-based IPv4 address browser to provide information about to what organizations each address block is allocated. The map now visualizes the whois allocation data; we thank the five regional internet registries for sharing this data with us and authorizing this visualization.

organizations in our Internet map

Finally, our web-based IPv4 address browser now has better time travel, with nearly 30 different census from Dec. 2005 to Nov. 2010, and we continue to update the map regularly.

Data collection for this work is through the LANDER project, and the map browser improvements are due to AMITE, both supported by DHS. Video preparation was supported by these projects and NSF through the MADCAT project.