On the morning of September 11th 2 commercial airliners
crashed into the World Trace Center towers in new York destroying
them, and another commercial airline crashed into the Pentagon.
Several people including journalists asked whether any impact in
Internet delays could be seen as a result of these events, e.g.
due to network congestion caused by increased use to search
for new stories etc.
We gathered the data from
the IEPM/PingER project for September 11th and imported into
We used Excel to plot various aggregate statistics including
the 25 percentile, median, 75 percentile 90 percentile and 95 prercentiles
of the Round Trip Tiime (RTT) measurements for each hour of the day.
The results are seen to the right, and it is observed taht there is no
sudden change in behavior following the event.
We also plotted the RTT as a function of
remote host pinged from SLAC (not all hosts are labelled in the
plot below), versus time of day (GMT) to see if
was any unusual change in behavior following the crashes.
The data includes over 200 hosts in over 70 countries.
For more on the deployment of PingER see
Each host is pinged
each half hour 11 times with 100 Byte pings and then 10 times with
1000 Byte pings. The first ping in each case is thrown away.
Most of the hosts are
on academic and research networks (such as internet 2, ESnet in the US
or JANet in the UK etc.) though it also includes several root servers
and about 10 .com hosts. The results for the RTT are
shown below. The hosts are ordered by the RTT for the 1st hour of the day.
It can be seen that there are no obvious
sudden sustained increases in the RTTs.
The deep valleys starting at about 14:00 GMT are due the loss of links to
sites on the Italian research and education network (INFN). The last
successful ping to infnge.ge.infn.it (in Genova) was about 6:33am PDT, and
the next attempt at 7:03am failed. According to CNN the first plane crashed into
the WTC tower just before 9am EDT or 6am PDT. It turns out that the links
from INFN to ESnet were located close to the World Trade Center. For example
60 Hudson Street a mjor peering point is about 0.6 mile away from the WTC site.
to Italy was restored between 9:00am and 9:30am September 12 '01, but the
RTT had increased from 175 msec to about 350 msec. The
new route was
through AlterNet. The route before the event
was direct from ESnet to
DANTE and GARR (the INFN ISP).
The raw data is available at:
See Attacks Lead To Internet Slowdowns
for more on the impact on the Internet at large.
Email from Mike Wilde [email@example.com], 9/12/01:
Les, it's sadly ironic that one of the people that made such robustness
possible was Daniel Lewin of Akamai, a victim of this tragedy.
For more on the impact of the WTC event on DANTE and European links, see:
Special update on the transatlantic situation
after Tuesday's events.
Email from Klaus Moeller Friday September 14, 2001.
First, let me express our heartfelt sorrows for the victims and their
relatives of the attack on the WTC, the Pentagon and the crashed
Now to the reason of my posting. This might be of interest as an
example, how the terrorist attack may also harm internet operations.
In second, it may help to explain, why some connectivity to Europe and
Germany may be bad.
The DFN was connected via two 622 Mbit/s links to the US part of the
internet. These links (and a link from TEN-155, the european backbone)
terminate at a Building in downtown Manhatten (60 Hudson St.). (They
start in Hannover and Frankfurt.)
The DFN point-of-presence (i.e. the point where DFN interlinks with
the US providers) is at the Telehouse in downtown Manhattan. Telehouse
and 60 Hudson St. are connected with a 10 Gbit/s fiber optic ring.
One half of the ring ran below WTC tower 1, the other half below WTC
tower 2. The Telehouse also host the DANTE POP. DANTE operates the
trans-european NREN backbone.
When the WTC collapsed, the 10 GB ring was severed in two places,
instantly cutting connectivity 60 Hudson street to and from the
Telehouse. Furthermore, the power was cut from Telehouse. Two days
later, the cooling unit of the emergency power generators gave out.
The DFN has a third, experimental 622 Mbit, link to a commercial US
provider. This link terminates somewhere else. All connectivity from
the DFN to the US is (sine tuesday) via this link. However, for all
european networks that can use only the DANTE transatlantic link,
connectivity to the US internet is lost due to the Telehouse power
outage. This will most likely hit the smaller (or poorer) european
Currently, work is underway to restore connectivity back to 2 * 622
Mbit, although it will, for obvious reasons, not be by repair of the
fiber optic link. Work is also underway to restore power to
Telehouse. About the plans of DANTE, I have no knowledge.
Klaus Moeller, DFN-CERT
Page owner: Les Cottrell